Fix two AudioFocus issues:

- if a focus owner abandons audio focus during a call, the next
 focus owner in the stack was never notified
- if a focus owner requests the focus while alread owning it, and
 the type of focus request changes, the previous focus owner was
 not notified that the type of focus loss had changed.

Change-Id: Iee6c6e17bcdd3c225a4b600f40ba434294870f17