net/mlx4: Make mlx4_is_eth visible inline funcion

Currently implemented as static function in resource_tracker.c --
this change will allow other files in mlx4_core to use it as well.

Signed-off-by: Ido Shamay <idos@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>