clusterer: make sure a discovered node is not added multiple times

Do not insert a new node into the list multiple times when:
* receiving multiple CLUSTERER_NODE_DESCRIPTION BIN messages
* we receive a CLUSTERER_NODE_DESCRIPTION message and the node also
  appears in CLUSTERER_FULL_TOP_UPDATE messages.

(cherry picked from commit b8e1075)

modules/clusterer/node_info.c

@@ -110,6 +110,11 @@ int add_node_info(node_info_t **new_info, cluster_info_t **cl_list, int *int_val
 		*cl_list = cluster;
 	}
 
+	if (get_node_by_id(cluster, int_vals[INT_VALS_NODE_ID_COL])) {
+		LM_DBG("Node [%d] already exists\n", int_vals[INT_VALS_NODE_ID_COL]);
+		return 0;
+	}
+
 	*new_info = shm_malloc(sizeof **new_info);
 	if (!*new_info) {
 		LM_ERR("no more shm memory\n");

modules/clusterer/topology.c

@@ -698,11 +698,6 @@ static node_info_t *add_node(bin_packet_t *received, cluster_info_t *cl,
 		lock_switch_read(cl_list_lock, lock_old_flag);
 		return NULL;
 	}
-	if (!new_node) {
-		LM_ERR("Unable to add node info to backing list\n");
-		lock_switch_read(cl_list_lock, lock_old_flag);
-		return NULL;
-	}
 
 	lock_switch_read(cl_list_lock, lock_old_flag);