Support backend reference counting

src/vmod_selector.c

@@ -434,6 +434,7 @@ vmod_set__fini(struct vmod_selector_set **setp)
 				struct entry *entry = set->table[i];
 				CHECK_OBJ_NOTNULL(entry,
 						  VMOD_SELECTOR_ENTRY_MAGIC);
+				VRT_Assign_Backend(&entry->backend, NULL);
 				free(entry->string);
 				FREE_OBJ(entry);
 				break;
@@ -515,7 +516,7 @@ vmod_set_add(VRT_CTX, struct vmod_selector_set *set,
 		set_added(set, n - 1, REGEX);
 	}
 	if (args->valid_backend) {
-		entry->backend = args->backend;
+		VRT_Assign_Backend(&entry->backend, args->backend);
 		set_added(set, n - 1, BACKEND);
 	}
 	if (args->valid_integer) {