kerndat: set uffd features to 0 before querying kernel

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>

criu/kerndat.c

@@ -722,6 +722,7 @@ int kerndat_uffd(void)
 {
 	int uffd;
 
+	kdat.uffd_features = 0;
 	uffd = uffd_open(0, &kdat.uffd_features);
 
 	/*