MT#63171 tcp: join threads after stop

Don't just signal them to stop but wait for them to actually stop.

Change-Id: I8f1ede904262bb8d0809ebfff3892da54e9a966f

core/sip/tcp_trsp.cpp

@@ -709,6 +709,7 @@ void tcp_server_socket::stop_threads()
 {
   for(unsigned int i=0; i<workers.size(); i++) {
     workers[i]->stop();
+    workers[i]->join();
   }
 }