core: more detailed error message when no config option to route requests

src/core/receive.c

@@ -306,7 +306,8 @@ int receive_msg(char *buf, unsigned int len, struct receive_info *rcv_info)
 		if(unlikely(main_rt.rlist[DEFAULT_RT] == NULL)) {
 			keng = sr_kemi_eng_get();
 			if(keng == NULL) {
-				LM_ERR("no config routing engine registered\n");
+				LM_ERR("no request_route {...} and no other config routing"
+						" engine registered\n");
 				goto error_req;
 			}
 			if(unlikely(cidlockset)) {