AP_Notify: grab initial flags state in init()

this prevents annoying tones on startup of APM:Plane

libraries/AP_Notify/ToneAlarm_PX4.cpp

@@ -41,6 +41,11 @@ bool ToneAlarm_PX4::init()
         hal.console->printf("Unable to open " TONEALARM_DEVICE_PATH);
         return false;
     }
+    
+    // set initial boot states. This prevents us issueing a arming
+    // warning in plane and rover on every boot
+    flags.armed = AP_Notify::flags.armed;
+    flags.failsafe_battery = AP_Notify::flags.failsafe_battery;
     return true;
 }
 
@@ -56,7 +61,7 @@ bool ToneAlarm_PX4::play_tune(const uint8_t tune_number)
 void ToneAlarm_PX4::update()
 {
     // exit immediately if we haven't initialised successfully
-    if (_tonealarm_fd <= 0 ) {
+    if (_tonealarm_fd == -1) {
         return;
     }
 

libraries/AP_Notify/ToneAlarm_PX4.h

@@ -26,13 +26,13 @@ public:
     /// init - initialised the tone alarm
     bool init(void);
 
-    /// play_tune - play one of the pre-defined tunes
-    bool play_tune(const uint8_t tune_number);
-
     /// update - updates led according to timed_updated.  Should be called at 50Hz
     void update();
 
 private:
+    /// play_tune - play one of the pre-defined tunes
+    bool play_tune(const uint8_t tune_number);
+
     int _tonealarm_fd;      // file descriptor for the tone alarm
 
     /// tonealarm_type - bitmask of states we track