uxrce_dds_client: immediately create data writers on startup

There is some race condition where in rare cases the topic publication
right after creating the writer did not get received on the ROS side.
This happens even with reliable QoS & reliable transport.

src/modules/uxrce_dds_client/uxrce_dds_client.cpp

@@ -366,6 +366,11 @@ bool UxrceddsClient::setupSession(uxrSession *session)
 		return false;
 	}
 
+	if (!_subs->init(session, _reliable_out, reliable_in, best_effort_in, _participant_id, _client_namespace)) {
+		PX4_ERR("subs init failed");
+		return false;
+	}
+
 	// create VehicleCommand replier
 	if (_num_of_repliers < MAX_NUM_REPLIERS) {
 		if (add_replier(new VehicleCommandSrv(session, _reliable_out, reliable_in, _participant_id, _client_namespace,
@@ -388,11 +393,6 @@ void UxrceddsClient::deleteSession(uxrSession *session)
 		_session_created = false;
 	}
 
-	if (_subs_initialized) {
-		_subs->reset();
-		_subs_initialized = false;
-	}
-
 	_last_payload_tx_rate = 0;
 	_timesync.reset_filter();
 }
@@ -650,9 +650,6 @@ void UxrceddsClient::run()
 		int poll_error_counter = 0;
 		resetConnectivityCounters();
 
-		_subs->init();
-		_subs_initialized = true;
-
 		while (!should_exit() && _connected) {
 			perf_begin(_loop_perf);
 			perf_count(_loop_interval_perf);