In the TX data path, prepend a special metadata ethertype which
instructs the hardware to perform cryptography.

In addition, 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 inverse of gso_size in the metadata.
This allows the FPGA to update the ESP header (seqno and seqiv) on the
resulting packets, by calculating the packet number within the GSO
back from the TCP sequence number.

Note that for GSO SKBs, the stack does not include an ESP trailer,
unlike the non-GSO case.
Signed-off-by: Ilan Tayari <ilant@mellanox.com>
Signed-off-by: Yossi Kuperman <yossiku@mellanox.com>
Signed-off-by: Yevgeny Kliteynik <kliteyn@mellanox.com>
Signed-off-by: Boris Pismenny <borisp@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>