vfio: Rename vfio_ioctl_check_extension()

To vfio_container_ioctl_check_extension().

A following patch will turn this into a non-static function, make it clear
it is related to the container.

Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/6-v3-297af71838d2+b9-vfio_container_split_jgg@nvidia.com


Signed-off-by: Alex Williamson <alex.williamson@redhat.com>