When stopping Hearing Aids, send Stop cmd to devices

This fixes the bug where the Stop command is not send to the Hearing
Aids devices which switching audio away from Hearing Aid.

Bug: 126465843
Test: Manual switching between A2DP and Hearing Aids while
playing audio.

Change-Id: Ifd8eaed7496e7e16c3948683c518d7627824d3e8