title: BLE gatt.discoverServices() returns true but Callback never fires
body: <p>I developed an App to connect to ble devices and exchange data.
  This works fine for my Smartphone (API Level 23). But when usind one with API leven 26, the <code>onServiceDiscovered</code> Callback never fires.<code>gatt.discoverServices()</code>
  returns true. I check with <code>newState == BluetoothProfile.STATE_CONNECTED</code>whether the connection was successful. After that I implemented a Delay before Starting de Service Discovery with</p>
  
  <pre><code>msecondHandler.postDelayed(new Runnable() {
                  @Override
                  public void run() {
                      boolean state = gatt.discoverServices();
                      Log.d(TAG,"State Service Discovered: "+state);
                  }
              },3000);
  </code></pre>
  
  <p>I changed the Delay withing 600 ms to 3000 ms but callback never fires.</p>