RDMA/mlx5: Set user priority for DCT

RDMA/mlx5: Set user priority for DCT

Currently, the driver doesn't set the PCP-based priority for DCT, hence
DCT response packets are transmitted without user priority.

Fix it by setting user provided priority in the eth_prio field in the DCT
context, which in turn sets the value in the transmitted packet.

Fixes: 776a3906b692 ("IB/mlx5: Add support for DC target QP")
Link: https://lore.kernel.org/r/5fd2d94a13f5742d8803c218927322257d53205c.1633512672.git.leonro@nvidia.com
Signed-off-by: Patrisious Haddad <phaddad@nvidia.com>
Reviewed-by: Maor Gottlieb <maorg@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>