For the older kernels the implementation of userfaultfd would not include
non-cooperative mode. In such case it is still possible to use uffd and
enable lazy-pages, but if the restored process will change its virtual
memory layout during restore, we'll get memory corruption.

After this change 'criu check --feature uffd' will report success if the kernel
supports userfaultfd at all and 'criu check --feature uffd-noncoop' will
report success if the kernel supports non-cooperative userfaultfd.
Suggested-by: Pavel Emelyanov <xemul@virtuozzo.com>
Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>