message: core: immediately send heartbeats after discovery
diff: @@ -266,12 +266,12 @@ void SystemImpl::system_thread()
  dl_time_t last_time{};
  while (!_should_exit) {
  - if (_time.elapsed_since_s(last_time) >= SystemImpl::_HEARTBEAT_SEND_INTERVAL_S) {
  if (_parent.is_connected()) {
  + if (_time.elapsed_since_s(last_time) >= SystemImpl::_HEARTBEAT_SEND_INTERVAL_S) {
  send_heartbeat();
  - }
  last_time = _time.steady_time();
  }
  + }
  _call_every_handler.run_once();
  _params.do_work();
  