Return an error if both EV_ENABLE and EV_DISABLE are specified for a kevent.

Currently, this combination results in EV_DISABLE being ignored.

Reviewed by:	kib
Sponsored by:	EMC / Isilon Storage Division
Differential Revision:	https://reviews.freebsd.org/D5307

sys/kern/kern_event.c

@@ -1116,6 +1116,9 @@ kqueue_register(struct kqueue *kq, struct kevent *kev, struct thread *td, int wa
 	int error, filt, event;
 	int haskqglobal, filedesc_unlock;
 
+	if ((kev->flags & (EV_ENABLE | EV_DISABLE)) == (EV_ENABLE | EV_DISABLE))
+		return (EINVAL);
+
 	fp = NULL;
 	kn = NULL;
 	error = 0;