allow tcp request with no dest, auto query topic.

lichao

2021-06-04 903b27f875e5f2a872c1b309f354b18c0450f35a

 src/exported_symbols

@@ -5,6 +5,7 @@
   BHUnregister;
   BHRegisterTopics;
   BHQueryTopicAddress;
   BHQueryProcs;
   BHSubscribeTopics;
   BHStartWorker;
   BHHeartbeatEasy;