Make sendVolumeUpdate method and VolumeAlias visible to ArcAudioService

- change mStreamVolumeAlias from private to protected
  ArcAudioService will use it to revert rescaled volume
- change sendVolumeUpdate method from private to protected
  ArcAudioService will override it to send request to the Host

Bug: 36129286
Test: Make such changes will allow ArcAudioService to successfully
      handle volume update requests.

Change-Id: I1e294d20187c6aa6d158a981814aa9b9a87a336c
1 file changed