audioservice: fix DTMF stream volume

DTMF stream must also be muted by silent mode when following ring
stream volume in order to be properly muted and unmuted when ringer
mode changes.

Also fix a problem in VolumeStreamState.setAllIndexes() when some
devices are not present in the stream state from which indexes
are copied.

Bug: 10932676.
Change-Id: I373d0fd1a475980786d97d97348d46a7e7421461