VolumeControl: Do not show volume bar on BT ON/OFF

With this patch we match BR/EDR behavior when it comes to showing volume bar.
It will not be shown on BT OFF/ON and when changing active LeAudio devices.

Bug: 311230051
Flag: Exempt, very simple fix affecting only Volume Bar for LeAudio
Test: Manual BT OFF/ON, switching active device
Test: mmm packages/modules/Bluetooth

Change-Id: I3f93d5629ddf7b25df5889b5b4b6ccb2a5fe1d0a