Plane: set AHRS vehicle class

ArduPlane/system.pde

@@ -472,6 +472,7 @@ static void startup_INS_ground(bool do_accel_init)
 
     ahrs.init();
     ahrs.set_fly_forward(true);
+    ahrs.set_vehicle_class(AHRS_VEHICLE_FIXED_WING);
     ahrs.set_wind_estimation(true);
 
     ins.init(style, ins_sample_rate);