AP_Vehicle: init safety state for SITL at boot

This allows BRD_SAFETY_DEFLT=1 to work correctly for SITL.

libraries/AP_Vehicle/AP_Vehicle.cpp

@@ -329,6 +329,11 @@ void AP_Vehicle::setup()
     }
 #endif
 
+#if CONFIG_HAL_BOARD == HAL_BOARD_SITL
+    // SITL needs the safety initialized manually if we want safety on at boot
+    hal.rcout->force_safety_on();
+#endif
+
 #if AP_SCHEDULER_ENABLED
     // initialise the main loop scheduler
     const AP_Scheduler::Task *tasks;