fanotify: allow userspace to flush all marks

fanotify is supposed to be able to flush all marks.  This is mostly useful
for the AV community to flush all cached decisions on a security policy
change.  This functionality has existed in the kernel but wasn't correctly
exposed to userspace.
Signed-off-by: Eric Paris <eparis@redhat.com>

include/linux/fanotify.h

@@ -52,7 +52,8 @@
 				 FAN_MARK_ONLYDIR |\
 				 FAN_MARK_MOUNT |\
 				 FAN_MARK_IGNORED_MASK |\
-				 FAN_MARK_IGNORED_SURV_MODIFY)
+				 FAN_MARK_IGNORED_SURV_MODIFY |\
+				 FAN_MARK_FLUSH)
 
 /*
  * All of the events - we build the list by hand so that we can add flags in