Fix bug 2201417. Whenever the System setting that indicates

whether the notifcation stream uses the ring volume changes, the
table of stream volume aliases in AudioService is updated. But the
name of the alias stored in VolumeStreamState.mVolumeIndexSettingName
was not updated whenever the NOTIFICATIONS_USE_RING_VOLUME setting
was updated. This caused the wrong volume setting to be persisted.
This change ensures the setting name is updated whenever the volume
alias is, and persists the notification volume change right away
(instead of after a delay), so that registered observers are notified
right away. The notification seekbar in the sound settings is an
example of such an observer.