AP_Scripting: use cached in AHRS_switch example

and use EKF2/EKF3, more likely to be useful

libraries/AP_Scripting/examples/AHRS_switch.lua

@@ -1,18 +1,21 @@
--- switch between DCM and EKF3 on a switch
+-- switch between EKF2 and EKF3 on a switch
 
----@diagnostic disable: need-check-nil
-
-local scripting_rc1 = rc:find_channel_for_option(300)
+local AUX_FUNCTION_NUM = 300
 local EKF_TYPE = Parameter('AHRS_EKF_TYPE')
 
 function update()
-   local sw_pos = scripting_rc1:get_aux_switch_pos()
-   if sw_pos == 0 then
+   local sw_pos = rc:get_aux_cached(AUX_FUNCTION_NUM)
+   if not sw_pos then
+      return update, 100
+   end
+   if sw_pos == 2 then
       EKF_TYPE:set(3)
    else
-      EKF_TYPE:set(0)
+      EKF_TYPE:set(2)
    end
    return update, 100
 end
 
+gcs:send_text(0, "Loaded AHRS switch for EKF3/EKF2")
+
 return update()