Add proper power save mode command format for MTS_DRAGONFLY_L471

Author: Leon

connectivity/cellular/source/framework/AT/AT_CellularDevice.cpp

@@ -559,7 +559,11 @@ nsapi_error_t AT_CellularDevice::set_power_save_mode(int periodic_time, int acti
 
         // request for both GPRS and LTE
 
+#ifdef TARGET_MTS_DRAGONFLY_L471QG
+        _at.at_cmd_discard("+CPSMS", "=1,,,", "%s%s", pt, at);
+#else
         _at.at_cmd_discard("+CPSMS", "=1,", "%s%s%s%s", pt, at, pt, at);
+#endif
 
         if (_at.get_last_error() != NSAPI_ERROR_OK) {
             tr_warn("Power save mode not enabled!");