net/mlx5: E-Switch, Use two priorities for SRIOV offloads mode

In the offloads mode, some slow path rules are added by the driver (e.g
send-to-vport), while offloaded rules are to be added from upper layers.

The slow path rules have lower priority and we don't want matching on
offloaded rules to suffer from extra steering hops related to the slow
path rules.

We use two priorities, one for offloaded rules (fast path), and one for
the control rules (slow path). To allow for that, we enable two priorities
for the FDB namespace in the FS core code.

Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>