lightningd/notification: use notification name in 'jsonrpc_notification_start()'

That way 'notification_topics' array modification would not lead to unwanted renaming

lightningd/notification.c

@@ -21,7 +21,7 @@ void notify_connect(struct lightningd *ld, struct node_id *nodeid,
 		    struct wireaddr_internal *addr)
 {
 	struct jsonrpc_notification *n =
-	    jsonrpc_notification_start(NULL, notification_topics[0]);
+	    jsonrpc_notification_start(NULL, "connect");
 	json_add_node_id(n->stream, "id", nodeid);
 	json_add_address_internal(n->stream, "address", addr);
 	jsonrpc_notification_end(n);
@@ -31,7 +31,7 @@ void notify_connect(struct lightningd *ld, struct node_id *nodeid,
 void notify_disconnect(struct lightningd *ld, struct node_id *nodeid)
 {
 	struct jsonrpc_notification *n =
-	    jsonrpc_notification_start(NULL, notification_topics[1]);
+	    jsonrpc_notification_start(NULL, "disconnect");
 	json_add_node_id(n->stream, "id", nodeid);
 	jsonrpc_notification_end(n);
 	plugins_notify(ld->plugins, take(n));
@@ -42,7 +42,7 @@ void notify_disconnect(struct lightningd *ld, struct node_id *nodeid)
 void notify_warning(struct lightningd *ld, struct log_entry *l)
 {
 	struct jsonrpc_notification *n =
-	    jsonrpc_notification_start(NULL, notification_topics[2]);
+	    jsonrpc_notification_start(NULL, "warning");
 	json_object_start(n->stream, "warning");
 	/* Choose "BROKEN"/"UNUSUAL" to keep consistent with the habit
 	 * of plugin. But this may confuses the users who want to 'getlog'
@@ -66,8 +66,8 @@ void notify_invoice_payment(struct lightningd *ld, struct amount_msat amount,
 			    struct preimage preimage, const struct json_escape *label)
 {
 	struct jsonrpc_notification *n =
-		jsonrpc_notification_start(NULL, notification_topics[3]);
-	json_object_start(n->stream, notification_topics[3]);
+		jsonrpc_notification_start(NULL, "invoice_payment");
+	json_object_start(n->stream, "invoice_payment");
 	json_add_string(n->stream, "msat",
 			type_to_string(tmpctx, struct amount_msat, &amount));
 	json_add_hex(n->stream, "preimage", &preimage, sizeof(preimage));