net/mlx5: Restrict metadata disablement to offloads mode

Now that there is clear separation for acl setup/cleanup between legacy
and offloads mode, limit metdata disablement to offloads mode.

Signed-off-by: Parav Pandit <parav@mellanox.com>
Reviewed-by: Vu Pham <vuhuong@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>