GCS_MAVLink: add AP_MAVLINK_BATTERY2_ENABLED define

on by default but can be turned off in next stable

libraries/GCS_MAVLink/GCS.h

@@ -289,7 +289,9 @@ public:
     void send_simstate() const;
     void send_sim_state() const;
     void send_ahrs();
+#if AP_MAVLINK_BATTERY2_ENABLED
     void send_battery2();
+#endif
 #if AP_OPTICALFLOW_ENABLED
     void send_opticalflow();
 #endif

libraries/GCS_MAVLink/GCS_Common.cpp

@@ -933,7 +933,9 @@ ap_message GCS_MAVLINK::mavlink_id_to_ap_message_id(const uint32_t mavlink_id) c
         { MAVLINK_MSG_ID_DISTANCE_SENSOR,       MSG_DISTANCE_SENSOR},
             // request also does report:
         { MAVLINK_MSG_ID_TERRAIN_REQUEST,       MSG_TERRAIN},
+#if AP_MAVLINK_BATTERY2_ENABLED
         { MAVLINK_MSG_ID_BATTERY2,              MSG_BATTERY2},
+#endif
         { MAVLINK_MSG_ID_CAMERA_FEEDBACK,       MSG_CAMERA_FEEDBACK},
 #if HAL_MOUNT_ENABLED
         { MAVLINK_MSG_ID_GIMBAL_DEVICE_ATTITUDE_STATUS, MSG_GIMBAL_DEVICE_ATTITUDE_STATUS},
@@ -2325,6 +2327,7 @@ void GCS::setup_uarts()
 #endif
 }
 
+#if AP_MAVLINK_BATTERY2_ENABLED
 // report battery2 state
 void GCS_MAVLINK::send_battery2()
 {
@@ -2342,6 +2345,7 @@ void GCS_MAVLINK::send_battery2()
     }
 #endif
 }
+#endif  // AP_MAVLINK_BATTERY2_ENABLED
 
 /*
   handle a SET_MODE MAVLink message
@@ -5468,10 +5472,12 @@ bool GCS_MAVLINK::try_send_message(const enum ap_message id)
         send_battery_status();
         break;
 
+#if AP_MAVLINK_BATTERY2_ENABLED
     case MSG_BATTERY2:
         CHECK_PAYLOAD_SIZE(BATTERY2);
         send_battery2();
         break;
+#endif
 
     case MSG_EKF_STATUS_REPORT:
         CHECK_PAYLOAD_SIZE(EKF_STATUS_REPORT);

libraries/GCS_MAVLink/GCS_config.h

@@ -5,3 +5,8 @@
 #ifndef HAL_GCS_ENABLED
 #define HAL_GCS_ENABLED 1
 #endif
+
+// BATTERY2 is slated to be removed:
+#ifndef AP_MAVLINK_BATTERY2_ENABLED
+#define AP_MAVLINK_BATTERY2_ENABLED 1
+#endif