Merge pull request FRRouting#16327 from FRRouting/mergify/bp/stable/1…

…0.0/pr-15716

isisd: Fix memory leaks when the transition of neighbor state from non-UP to DOWN (backport FRRouting#15716)

isisd/isis_adjacency.c

@@ -358,12 +358,15 @@ void isis_adj_state_change(struct isis_adjacency **padj,
 				 * purposes */
 				adj->last_flap = time(NULL);
 				adj->flaps++;
-			} else if (old_state == ISIS_ADJ_UP) {
-				circuit->adj_state_changes++;
+			} else {
+				if (old_state == ISIS_ADJ_UP) {
+					circuit->adj_state_changes++;
 
-				circuit->upadjcount[level - 1]--;
-				if (circuit->upadjcount[level - 1] == 0)
-					isis_tx_queue_clean(circuit->tx_queue);
+					circuit->upadjcount[level - 1]--;
+					if (circuit->upadjcount[level - 1] == 0)
+						isis_tx_queue_clean(
+							circuit->tx_queue);
+				}
 
 				if (new_state == ISIS_ADJ_DOWN) {
 					listnode_delete(
@@ -409,10 +412,13 @@ void isis_adj_state_change(struct isis_adjacency **padj,
 						master, send_l2_csnp, circuit,
 						0, &circuit->t_send_csnp[1]);
 				}
-			} else if (old_state == ISIS_ADJ_UP) {
-				circuit->upadjcount[level - 1]--;
-				if (circuit->upadjcount[level - 1] == 0)
-					isis_tx_queue_clean(circuit->tx_queue);
+			} else {
+				if (old_state == ISIS_ADJ_UP) {
+					circuit->upadjcount[level - 1]--;
+					if (circuit->upadjcount[level - 1] == 0)
+						isis_tx_queue_clean(
+							circuit->tx_queue);
+				}
 
 				if (new_state == ISIS_ADJ_DOWN) {
 					if (adj->circuit->u.p2p.neighbor == adj)