Camera: Track number of completed events

Closes #3903

libraries/AP_Camera/AP_Camera.cpp

@@ -258,7 +258,7 @@ void AP_Camera::send_feedback(mavlink_channel_t chan)
         current_loc.lat, current_loc.lng,
         altitude*1e-2, altitude_rel*1e-2,
         ahrs.roll_sensor*1e-2, ahrs.pitch_sensor*1e-2, ahrs.yaw_sensor*1e-2,
-        0.0f,CAMERA_FEEDBACK_PHOTO);
+        0.0f, CAMERA_FEEDBACK_PHOTO, _feedback_events);
 }
 
 
@@ -441,6 +441,7 @@ void AP_Camera::update_trigger()
 {
     trigger_pic_cleanup();
     if (check_trigger_pin()) {
+        _feedback_events++;
         gcs().send_message(MSG_CAMERA_FEEDBACK);
         DataFlash_Class *df = DataFlash_Class::instance();
         if (df != nullptr) {

libraries/AP_Camera/AP_Camera.h

@@ -98,6 +98,7 @@ private:
     uint32_t        _last_photo_time;   // last time a photo was taken
     struct Location _last_location;
     uint16_t        _image_index;       // number of pictures taken since boot
+    uint16_t        _feedback_events;   // number of feedback events since boot
 
     // pin number for accurate camera feedback messages
     AP_Int8         _feedback_pin;