center restart with new shm; set center node ssn.

lichao

2021-06-02 993c556000a414011626770540678948f16eaa9e

 src/topic_node.h

@@ -39,7 +39,7 @@
   const MQInfo &BusAddr() const { return BHTopicBusAddress(shm()); }

public:
   TopicNode(SharedMemory &shm);
   TopicNode(SharedMemory &shm, MQId ssn_id = 0);
   ~TopicNode();

   // topic node