Plane: Add compass cal capability bit

ArduPlane/capabilities.cpp

@@ -7,6 +7,7 @@ void Plane::init_capabilities(void)
                                MAV_PROTOCOL_CAPABILITY_COMMAND_INT |
                                MAV_PROTOCOL_CAPABILITY_MISSION_INT |
                                MAV_PROTOCOL_CAPABILITY_SET_POSITION_TARGET_GLOBAL_INT |
-                               MAV_PROTOCOL_CAPABILITY_SET_ATTITUDE_TARGET);
+                               MAV_PROTOCOL_CAPABILITY_SET_ATTITUDE_TARGET |
+                               MAV_PROTOCOL_CAPABILITY_COMPASS_CALIBRATION);
 
 }