Plane: enable failsafe battery reporting

ArduPlane/ArduPlane.pde

@@ -741,6 +741,7 @@ void setup() {
     notify.init();
     AP_Notify::flags.armed = true;
     AP_Notify::flags.pre_arm_check = true;
+    AP_Notify::flags.failsafe_battery = false;
 
     rssi_analog_source = hal.analogin->channel(ANALOG_INPUT_NONE);
 

ArduPlane/events.pde

@@ -112,6 +112,7 @@ void low_battery_event(void)
     set_mode(RTL);
     aparm.throttle_cruise.load();
     battery.low_batttery = true;
+    AP_Notify::flags.failsafe_battery = true;
 }
 
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