net/mlx5: Expose port.c/mlx5_query_module_num() function

Make mlx5_query_module_num() defined in port.c, a non-static, so it can
be used by other files.

CC: Jean Delvare <jdelvare@suse.com>
CC: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Adham Faris <afaris@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Reviewed-by: Gal Pressman <gal@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://lore.kernel.org/r/20230807180507.22984-2-saeed@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>