title: BluetoothGattCallback's onCharacteristicChanged not triggered on Android 7.1.1
body: <p>When communicating with my BLE device <code>onCharacteristicChanged</code> is trigged as expected for all versions of android prior to Android N. The issue is seen only on Android N.</p>
  
  <p>For Android N <code>onCharacteristicChanged</code> is never triggered. Is there something that has changed in the way <code>BluetoothGattCallback</code> behaves on Android Nougat?</p>
  
  <p>Initialization of descriptor:</p>
  
  <pre><code>BluetoothGattDescriptor descriptor = characteristic.getDescriptor(MyDeviceUuid.CHARACTERISTIC_UPDATE_NOTIFICATION_DESCRIPTOR_UUID);
  if (descriptor != null) {
              descriptor.setValue(enable ? BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE : BluetoothGattDescriptor.DISABLE_NOTIFICATION_VALUE);
              mBluetoothGatt.writeDescriptor(descriptor);
          }
  </code></pre>