net/mlx5e: Set per priority hairpin pairs

As part of the QoS model, on xmit, the HW mandates that all packets going
through a given SQ have the same priority. To align hairpin SQs with that,
we use the priority given as part of the matching for the hairpin hash key.

This ensures that flows/packets mapped to different HW priorities will
go through different hairpin instances. If no priority is given for
matching, we treat that as an 8th priority, this is in order not to
harm cases where priority is specified.

Only the PCP priority trust model is supported.

Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>