don't recreate callback at each scan to avoid memory consumption

#173

ZgatewayBT.ino

@@ -118,6 +118,7 @@ Thanks to wolass https://github.com/wolass for suggesting me HM 10 and dinosd ht
                           NULL,       /* Task handle. */
                           taskCore);  /* Core where the task should run */
         trc(F("ZgatewayBT ESP32 setup done "));    
+        BLEDevice::init("");             
     }
 
     void coreTask( void * pvParameters ){
@@ -128,9 +129,9 @@ Thanks to wolass https://github.com/wolass for suggesting me HM 10 and dinosd ht
         while(true){
             trc(taskMessage);
             delay(TimeBtw_Read);
-            BLEDevice::init("");
             BLEScan* pBLEScan = BLEDevice::getScan(); //create new scan
-            pBLEScan->setAdvertisedDeviceCallbacks(new MyAdvertisedDeviceCallbacks());
+            MyAdvertisedDeviceCallbacks myCallbacks;
+            pBLEScan->setAdvertisedDeviceCallbacks(&myCallbacks);
             pBLEScan->setActiveScan(true); //active scan uses more power, but get results faster
             BLEScanResults foundDevices = pBLEScan->start(Scan_duration);
         }