net/mlx5: TX WQE Add trailer insertion field

Add new TX WQE field for Connect-X6DX trailer insertion support,
when set, the HW adds a trailer to the packet, the WQE trailer
association flags are used to set to HW the header which the
trailer belongs.

Signed-off-by: Raed Salem <raeds@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>