net/mlx5: E-Switch, add a new prio to be used by the RDMA side

Create a new prio in the FDB, it will be used when inserting steering rules
into the FDB from the RDMA side. We create a new PRIO so rules from the
net side and rules from the RDMA side won't be inserted to the same PRIO,
each side has it's own sandbox to play in.

Signed-off-by: Mark Bloch <markb@mellanox.com>
Reviewed-by: Maor Gottlieb <maorg@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>