Fix a MAC label leak for POSIX semaphores, in which per-policy labels

would be properly disposed of, but the global label structure for the
semaphore wouldn't be freed.

MFC after:	3 days
Reported by:	tanyong <tanyong at ercist dot iscas dot ac dot cn>,
		zhouzhouyi

sys/security/mac/mac_posix_sem.c

@@ -72,6 +72,7 @@ mac_posixsem_label_free(struct label *label)
 {
 
 	MAC_PERFORM(posixsem_destroy_label, label);
+	mac_labelzone_free(label);
 }
 
 void