In the TX data path, spot packets with xfrm stack IPsec offload
indication.

Fill Software-Parser segment in TX descriptor so that the hardware
may parse the ESP protocol, and perform TX checksum offload on the
inner payload.

Support GSO, by providing the trailer data and ICV placeholder
so HW can fill it post encryption operation.

Padding alignment cannot be performed in HW (ConnectX-6Dx) due to
a bug. Software can overcome this limitation by adding NETIF_F_HW_ESP to
the gso_partial_features field in netdev so the packets being
aligned by the stack.

l4_inner_checksum cannot be offloaded by HW for IPsec tunnel type packet.

Note that for GSO SKBs, the stack does not include an ESP trailer,
unlike the non-GSO case.

Below is the iperf3 performance report on two server of 24 cores
Intel(R) Xeon(R) CPU E5-2620 v3 @ 2.40GHz with ConnectX6-DX.
All the bandwidth test uses iperf3 TCP traffic with packet size 128KB.
Each tunnel uses one iperf3 stream with one thread (option -P1).
TX crypto offload shows improvements on both bandwidth
and CPU utilization.

----------------------------------------------------------------------
Mode            |  Num tunnel | BW     | Send CPU util | Recv CPU util
                |             | (Gbps) | (Average %)   | (Average %)
----------------------------------------------------------------------
Cryto offload   |             |        |               |
(RX only)       | 1           | 4.7    | 4.2           | 3.5
----------------------------------------------------------------------
Cryto offload   |             |        |               |
(RX only)       | 24          | 15.6   | 20            | 10
----------------------------------------------------------------------
Non-offload     | 1           | 4.6    | 4             | 5
----------------------------------------------------------------------
Non-offload     | 24          | 11.9   | 16            | 12
----------------------------------------------------------------------
Cryto offload   |             |        |               |
(TX & RX)       | 1           | 11.9   | 2.1           | 5.9
----------------------------------------------------------------------
Cryto offload   |             |        |               |
(TX & RX)       | 24          | 38     | 9.5           | 27.5
----------------------------------------------------------------------
Cryto offload   |             |        |               |
(TX only)       | 1           | 4.7    | 0.7           | 5
----------------------------------------------------------------------
Cryto offload   |             |        |               |
(TX only)       | 24          | 14.5   | 6             | 20

Regression tests show no degradation on non-ipsec and
non-offload-ipsec traffics. The packet rate test uses pktgen UDP to
transmit on single CPU, the instructions and cycles are measured on
the transmit CPU.

before:
----------------------------------------------------------------------
Non-offload             | 1           | 4.7    | 4.2           | 5.1
----------------------------------------------------------------------
Non-offload             | 24          | 11.2   | 14            | 15
----------------------------------------------------------------------
Non-ipsec               | 1           | 28     | 4             | 5.7
----------------------------------------------------------------------
Non-ipsec               | 24          | 68.3   | 17.8          | 39.7
----------------------------------------------------------------------
Non-ipsec packet rate(BURST=1000 BC=5 NCPUS=1 SIZE=60)
13.56Mpps, 456 instructions/pkt, 191 cycles/pkt

after:
----------------------------------------------------------------------
Non-offload             | 1           | 4.69    | 4.2          | 5
----------------------------------------------------------------------
Non-offload             | 24          | 11.9   | 13.5          | 15.1
----------------------------------------------------------------------
Non-ipsec               | 1           | 29     | 3.2           | 5.5
----------------------------------------------------------------------
Non-ipsec               | 24          | 68.2   | 18.5          | 39.8
----------------------------------------------------------------------
Non-ipsec packet rate: 13.56Mpps, 472 instructions/pkt, 191 cycles/pkt
Signed-off-by: Raed Salem <raeds@mellanox.com>
Signed-off-by: Huy Nguyen <huyn@mellanox.com>
Reviewed-by: Maxim Mikityanskiy <maximmi@mellanox.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>