When run command "iw dev wlan0 station dump", the rx duration is 0.
When firmware indicate WMI_UPDATE_STATS_EVENTID, extended flag of
statsis not set by default, so firmware do not report rx duration.

one sample:
localhost # iw wlan0 station dump
Station c4:04:15:5d:97:22 (on wlan0)
        inactive time:  48 ms
        rx bytes:       21670
        rx packets:     147
        tx bytes:       11529
        tx packets:     100
        tx retries:     88
        tx failed:      36
        beacon loss:    1
        beacon rx:      31
        rx drop misc:   47
        signal:         -72 [-74, -75] dBm
        signal avg:     -71 [-74, -75] dBm
        beacon signal avg:      -71 dBm
        tx bitrate:     54.0 MBit/s MCS 3 40MHz
        rx bitrate:     1.0 MBit/s
	rx duration:    0 us

This patch enable firmware's extened flag of stats by setting flag
WMI_TLV_STAT_PEER_EXTD of ar->fw_stats_req_mask which is set in
ath10k_core_init_firmware_features via WMI_REQUEST_STATS_CMDID.

After apply this patch, rx duration show value with the command:
Station c4:04:15:5d:97:22 (on wlan0)
        inactive time:  883 ms
        rx bytes:       44289
        rx packets:     265
        tx bytes:       10838
        tx packets:     93
        tx retries:     899
        tx failed:      103
        beacon loss:    0
        beacon rx:      78
        rx drop misc:   46
        signal:         -71 [-74, -76] dBm
        signal avg:     -70 [-74, -76] dBm
        beacon signal avg:      -70 dBm
        tx bitrate:     54.0 MBit/s MCS 3 40MHz
        rx bitrate:     1.0 MBit/s
        rx duration:    358004 us

This patch do not have side effect for all chips, because function
ath10k_debug_fw_stats_request is already exported to debugfs
"fw_stats" and WMI_REQUEST_STATS_CMDID is safely sent after condition
checked by ath10k_peer_stats_enabled in ath10k_sta_statistics.

Tested with QCA6174 SDIO with firmware WLAN.RMH.4.4.1-00042.
Signed-off-by: Wen Gong <wgong@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200423022758.5365-1-wgong@codeaurora.org