[VTOL] impose minimum transition duration

* VT_F_TR_OL_TM would silently reduce VT_TRANS_MIN_TM when VT_F_TR_OL_TM was smaller

src/modules/vtol_att_control/vtol_att_control_main.cpp

@@ -274,12 +274,14 @@ VtolAttitudeControl::parameters_update()
 	param_get(_params_handles.front_trans_time_min, &_params.front_trans_time_min);
 
 	/*
-	 * Minimum transition time can be maximum 90 percent of the open loop transition time,
+	 * Open loop transition time needs to be larger than minimum transition time,
 	 * anything else makes no sense and can potentially lead to numerical problems.
 	 */
-	_params.front_trans_time_min = math::min(_params.front_trans_time_openloop * 0.9f,
-				       _params.front_trans_time_min);
-
+	if (_params.front_trans_time_openloop < _params.front_trans_time_min * 1.1f) {
+		_params.front_trans_time_openloop = _params.front_trans_time_min * 1.1f;
+		param_set_no_notification(_params_handles.front_trans_time_openloop, &_params.front_trans_time_openloop);
+		mavlink_log_critical(&_mavlink_log_pub, "OL transition time set larger than min transition time");
+	}
 
 	param_get(_params_handles.front_trans_duration, &_params.front_trans_duration);
 	param_get(_params_handles.back_trans_duration, &_params.back_trans_duration);