net/mlx5: fix tunnel flow priority

net/mlx5: fix tunnel flow priority

PMD flow priority is different from application flow priority.  Flow
rules with higher match granularity assigned higher PMD priority. Also
PMD splits internally RSS flows according to flow RSS layer.

Final PMD flow rule priority derived from the last match item network
level, after PMD adjusts flow rule, where L4 match gets the highest
priority and L2 the lowest.

The patch adjusts tunnels flow rule priority calculation for PMDs
running verb API.

Introduce MLX5_TUNNEL_PRIO_GET macro.

Fixes: 4a78c88e3bae ("net/mlx5: fix Verbs flow tunnel")
Cc: stable@dpdk.org
Signed-off-by: Gregory Etelson <getelson@mellanox.com>
Acked-by: Matan Azrad <matan@mellanox.com>
Acked-by: Ori Kam <orika@mellanox.com>