Use mode_request for RC mode switching

msg/CMakeLists.txt

@@ -109,6 +109,7 @@ set(msg_files
 	mavlink_log.msg
 	mission.msg
 	mission_result.msg
+	mode_request.msg
 	mount_orientation.msg
 	multirotor_motor_limits.msg
 	navigator_mission_item.msg

msg/mode_request.msg

@@ -0,0 +1,7 @@
+uint64 timestamp # time since system start (microseconds)
+
+uint8 mode # what mode is requested according to commander_state.MAIN_STATE_
+
+uint8 source # how the request was triggered
+uint8 SOURCE_RC_MODE_SLOT = 0
+uint8 SOURCE_RC_SWITCH = 1