RDMA/mlx5: Add NIC TX steering support

Just like ingress steering, allow a user to create steering rules that
match egress vport traffic. We expose the same number of priorities as
the bypass (NIC RX) steering.

Signed-off-by: Mark Bloch <markb@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>