Plane: inform dataflash of vehicle arm state

ArduPlane/ArduPlane.cpp

@@ -151,11 +151,17 @@ void Plane::loop()
     scheduler.run(loop_us);
 }
 
+void Plane::update_soft_armed()
+{
+    hal.util->set_soft_armed(arming.is_armed() &&
+                             hal.util->safety_switch_state() != AP_HAL::Util::SAFETY_DISARMED);
+    DataFlash.set_vehicle_armed(hal.util->get_soft_armed());
+}
+
 // update AHRS system
 void Plane::ahrs_update()
 {
-    hal.util->set_soft_armed(arming.is_armed() &&
-                   hal.util->safety_switch_state() != AP_HAL::Util::SAFETY_DISARMED);
+    update_soft_armed();
 
 #if HIL_SUPPORT
     if (g.hil_mode == 1) {

ArduPlane/Plane.h

@@ -1095,6 +1095,7 @@ private:
     void parachute_release();
     bool parachute_manual_release();
     void accel_cal_update(void);
+    void update_soft_armed();
 
     // support for AP_Avoidance custom flight mode, AVOID_ADSB
     bool avoid_adsb_init(bool ignore_checks);

ArduPlane/system.cpp

@@ -815,8 +815,7 @@ int8_t Plane::throttle_percentage(void)
 void Plane::change_arm_state(void)
 {
     Log_Arm_Disarm();
-    hal.util->set_soft_armed(arming.is_armed() &&
-                             hal.util->safety_switch_state() != AP_HAL::Util::SAFETY_DISARMED);
+    update_soft_armed();
     quadplane.set_armed(hal.util->get_soft_armed());
 }