Sub: fix RC init order to avoid error message

ArduSub/system.cpp

@@ -62,8 +62,9 @@ void Sub::init_ardupilot()
 #endif
 
     // initialise rc channels including setting mode
-    rc().init();
     rc().convert_options(RC_Channel::AUX_FUNC::ARMDISARM_UNUSED, RC_Channel::AUX_FUNC::ARMDISARM);
+    rc().init();
+
 
     init_rc_in();               // sets up rc channels from radio
     init_rc_out();              // sets up motors and output to escs