IB/mlx5: Don't create IB instance over Ethernet ports

Since we still don't have RoCE support in mlx5, avoid
creating IB driver instance over Ethernet ports.

Signed-off-by: Majd Dibbiny <majd@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>