Currently we set some cell tunable parameters on the cell object itself
(e.g. dl_earfcn), while other cell tunable parameters on the
cell_default object, e.g. cell bandwidth. This works ok when there is
only one cell, but with multiple cells it makes a problem because
different cells can have e.g. different bandwidth.

So as preparatory step for MultiRU move the code, that sets tunable
parameters for lte cells, from cell_default to cell object itself.

Rendered config changes but we can verify that the configuration, that
enb actually uses, stays the same: When enb starts it builds internal
configuration for all configured cell objects by merging cell_default +
cell's explicit configuration and using the result as the actual
configuration for the cell. There is no more cell_default in that actual
configuration. And also enb emits that actual runtime configuration in
the beginning of enb.log which we can extract and investigate(*)

So this way we can run enb with old and new generated enb.cfg and then
compare the actual configuration. It turns out to be empty:

    ~/enb# ./lteenb -n x/old/enb.cfg
    ...
    RF0: sample_rate=11.520 MHz dl_freq=1910.000 MHz ul_freq=1910.000 MHz (band 33) dl_ant=2 ul_ant=2
    (enb) quit
    ~/enb# mv log/enb.log log/enb.log.old

    ~/enb# ./lteenb -n x/out/enb.cfg
    ...
    RF0: sample_rate=11.520 MHz dl_freq=1910.000 MHz ul_freq=1910.000 MHz (band 33) dl_ant=2 ul_ant=2
    (enb) quit
    ~/enb# mv log/enb.log log/enb.log.new

    ~/enb# ../ots/json_util log log/enb.log.old >a
    ~/enb# ../ots/json_util log log/enb.log.new >b
    ~/enb# diff -u a b  # output is empty

which means that effective enb configuration before and after this patch is exactly the same.

For the reference, how internal configuration looks like is provided in the appendix.

(*) see https://tech-academy.amarisoft.com/ExtractConfigFromLog.html for details.

/cc @lu.xu, @tomo, @xavier_thompson, @Daetalus
/reviewed-by @jhuge
/reviewed-on !1515

P.S. for now I do not plan to expose full measurement configuration in
     the generic MultiRU and so it stays in cell_default with corresponding TODO.

--------

Appendix. Dump of internal enb configuration for enb.cfg before and after the patch

```
$ ../ots/json_util log log/enb.log.old
```

```json
{
    "cell_list": [
        {
            "cell_barred": false,
            "cell_id": 0,
            "cipher_algo_pref": [],
            "cqi_period": 40,
            "cyclic_prefix": "normal",
            "dl_256qam": true,
            "dl_earfcn": 36100,
            "dpc": true,
            "dpc_pucch_snr_target": 25,
            "dpc_pusch_snr_target": 25,
            "drb_config": [ ... ],		# removed for brevity
            "ho_from_meas": true,
            "inactivity_timer": 10000,
            "initial_cqi": 3,
            "integ_algo_pref": [2, 1],
            "intra_freq_reselection": true,
            "m_ri": 8,
            "mac_config": {
                "dl_max_harq_tx": 5,
                "ul_max_harq_tx": 5
            },
            "manual_ref_signal_power": true,
            "meas_config_desc": {
                "a1_hysteresis": 0,
                "a1_report_type": "rsrp",
                "a1_rsrp": -70,
                "a1_time_to_trigger": 640,
                "a2_hysteresis": 0,
                "a2_report_type": "rsrp",
                "a2_rsrp": -80,
                "a2_time_to_trigger": 640,
                "a3_hysteresis": 0,
                "a3_offset": 6,
                "a3_report_type": "rsrp",
                "a3_time_to_trigger": 480
            },
            "meas_gap_config": "gp0",
            "n_antenna_dl": 2,
            "n_antenna_ul": 2,
            "n_id_cell": 0,
            "n_rb_dl": 50,
            "n_symb_cch": 0,
            "pdcch_format": 2,
            "pdsch_dedicated": {
                "p_a": -3,
                "p_b": -1
            },
            "phich_duration": "normal",
            "phich_resource": "1",
            "plmn_list": ["00101"],
            "prach_config_index": 4,
            "prach_freq_offset": -1,
            "pucch_dedicated": {
                "cqi_pucch_n_rb": 1,
                "n1_pucch_sr_count": 11,
                "tdd_ack_nack_feedback_mode": "multiplexing"
            },
            "pusch_dedicated": {
                "beta_offset_ack_index": 9,
                "beta_offset_cqi_index": 6,
                "beta_offset_ri_index": 6
            },
            "pusch_hopping_offset": -1,
            "pusch_max_its": 6,
            "pusch_msg3_mcs": 0,
            "q_rx_lev_min": -70,
            "rf_port": 0,
            "root_sequence_index": 204,
            "scell_list": [],
            "si_coderate": 0.2,
            "si_pdcch_format": 2,
            "si_value_tag": 0,
            "si_window_length": 40,
            "sib_sched_list": [ ... ],		# remove for brevity
            "sp_config": 7,
            "sr_period": 20,
            "srb_config": [
                {
                    "id": 1,
                    "maxRetxThreshold": 32,
                    "t_PollRetransmit": 60,
                    "t_Reordering": 45
                },
                {
                    "id": 2,
                    "maxRetxThreshold": 32,
                    "t_PollRetransmit": 60,
                    "t_Reordering": 45
                }
            ],
            "srs_dedicated": {
                "srs_bandwidth": 2,
                "srs_bandwidth_config": 2,
                "srs_hopping_bandwidth": 0,
                "srs_period": 40,
                "srs_subframe_config": 3
            },
            "tac": 1,
            "transmission_mode": 3,
            "ul_64qam": true,
            "uldl_config": 6
        }
    ],
    "com_addr": "127.0.1.2:9001",
    "enb_id": 107216,
    "gtp_addr": "127.0.1.1",
    "log_filename": "log/enb.log",
    "log_options": "all.level=error,all.max_size=0,nas.level=debug,nas.max_size=1,s1ap.level=debug,s1ap.max_size=1,x2ap.level=debug,x2ap.max_size=1,rrc.level=debug,rrc.max_size=1,phy.level=info,file.rotate=1G,file.path=/dev/null",
    "mme_list": [
        {
            "mme_addr": "127.0.1.100"
        }
    ],
    "rf_driver": {
        "args": "dev0=/dev/sdr0",
        "name": "sdr",
        "realtime": 1,
        "rx_antenna": "tx_rx",
        "tdd_tx_mod": 1
    },
    "rx_gain": 43,
    "tx_gain": 62
}
```