When there is a stale kdat cache file it's contents is read into the memory
and we end up requesting random userfaultfd features. Explicitly set the
kdat.uffd_features to zero before querying the kernel resolves the issue.

✓ travis-ci: success for kerndat: set uffd features to 0 before querying kernel
Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>