AudioService: Fix mute issue when changing audio routes

When audio device routing changes, verify that streams now routed via
fixed/full volume properly update volume index and mute state to ensure
the user does not get into a state where the stream is muted, but full
volume behavior does not allow mute changes.

AudioService#onObserveDevicesForAllStreams() is called as a result of AudioDeviceInventory#onReportNewRoutes().

Bug: 162480816
Test: see repro on bug with muting/unmuting scenario
Change-Id: I60b3b75a3ccb4a0d68ea797d177abb032f82bb91