filt_fsevent: only record interested events

Respect filter-specific flags for the EVFILT_FS filter.

When a kevent is registered with the EVFILT_FS filter, it is always
triggered when an EVFILT_FS event occurs, regardless of the
filter-specific flags used. Fix that.

Reviewed by:	kib
Differential Revision:	https://reviews.freebsd.org/D28974

sys/kern/vfs_subr.c

@@ -6016,7 +6016,8 @@ static int
 filt_fsevent(struct knote *kn, long hint)
 {
 
-	kn->kn_fflags |= hint;
+	kn->kn_fflags |= kn->kn_sfflags & hint;
+
 	return (kn->kn_fflags != 0);
 }