observer should exit if listen rpc port failed

deps/oblib/src/rpc/obrpc/ob_poc_rpc_server.cpp

@@ -152,12 +152,13 @@ int ObPocRpcServer::start(int port, int net_thread_count, frame::ObReqDeliver* d
   int lfd = -1;
   int grp = 1;
   if ((lfd = pn_listen(port, serve_cb)) == -1) {
-    ret = OB_IO_ERROR;
+    ret = OB_SERVER_LISTEN_ERROR;
     RPC_LOG(ERROR, "pn_listen failed", K(ret));
   } else {
     global_deliver = deliver;
     int count = pn_provision(lfd, grp, net_thread_count);
     if (count != net_thread_count) {
+      ret = OB_ERR_SYS;
       RPC_LOG(WARN, "pn_provision error", K(count), K(net_thread_count));
     }
     has_start_ = true;

deps/oblib/src/rpc/pnio/interface/group.c

@@ -82,7 +82,7 @@ PN_API int pn_listen(int port, serve_cb_t cb)
   pn_listen_t* pnl = locate_listen(idx);
   addr_t addr;
   addr_init(&addr, "0.0.0.0", port);
-  if (listen_init(&pnl->l, addr, pnl_dispatch_accept) < 0) {
+  if (listen_init(&pnl->l, addr, pnl_dispatch_accept) != 0) {
     idx = -1;
   } else {
     pnl->serve_cb = cb;