SITL: added SIM_MAG_SCALING for testing scale factor errors

libraries/SITL/SITL.cpp

@@ -202,6 +202,8 @@ const AP_Param::GroupInfo SITL::var_info2[] = {
 
     AP_GROUPINFO("SAFETY_STATE",    59, SITL,  _safety_switch_state, 0),
 
+    AP_GROUPINFO("MAG_SCALING",    60, SITL,  mag_scaling, 1),
+
     AP_GROUPEND
 
 };

libraries/SITL/SITL.h

@@ -184,6 +184,7 @@ public:
     AP_Int8  baro_count; // number of simulated baros to create
     AP_Int8 gps_hdg_enabled; // enable the output of a NMEA heading HDT sentence
     AP_Int32 loop_delay; // extra delay to add to every loop
+    AP_Float mag_scaling; // scaling factor on first compasses
 
     // EFI type
     enum EFIType {