IB/mlx5: Support setting Ethernet priority for Raw Packet QPs

When the user changes the Address Vector(AV) in the modify QP, he
provides an SL. This SL should be translated to Ethernet Priority
by taking the 3 LSB bits, and modify the QP's TIS according to this
Ethernet priority.

Signed-off-by: Majd Dibbiny <majd@mellanox.com>
Reviewed-by: Matan Barak <matanb@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>