AudioService: fix settings for fixed volume device

Force max volume for devices with fixed volume policy (HDMI, dock...)
when reading the settings from DB. Otherwise, these devices would
get the default volume which is not what we want.

Also fix a problem related to ringer mode management when reloading the
volume settings upon user switch that would cause a muted stream to be
unmuted.

Bug 7301563;

Change-Id: I81cdb97125b845da584ed680181b93c7c1e5903f