Fix <Report Audio Status> update

Even if the "SystemAudioMode" is OFF, when television device receives
<Report Audio Status> notification from AVR, the volume of the
television device will be changed.

Ignore <Report Audio Status> when the "SystemAudioMode" is OFF
to avoid unnecessary audio service's update.

Test: Send <Report Audio Status> command from source device such as
      AVR when the "SystemAudioMode" is off.

Change-Id: I2e5414390870f0db38973abce9cb69136b686112