Tracker: fix RC init order to avoid error message

AntennaTracker/system.cpp

@@ -59,8 +59,8 @@ void Tracker::init_ardupilot()
     serial_manager.set_blocking_writes_all(false);
 
     // initialise rc channels including setting mode
-    rc().init();
     rc().convert_options(RC_Channel::AUX_FUNC::ARMDISARM_UNUSED, RC_Channel::AUX_FUNC::ARMDISARM);
+    rc().init();
 
     // initialise servos
     init_servos();