net/mlx5: Unexport functions that need not be exported

mlx5_query_vport_state() and mlx5_modify_vport_admin_state() are used
only from within mlx5_core  - unexport them.

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