Fix issue 2456968: Alarm rings in "silent mode and when Alarm in silent mode is turned off".

The problem is that even if silent mode is active, changing the alarm volume will change current
alarm stream volume. This is true for other stream types affected by ringer mode (ring, notification...) but
the UI design is such that it is not possible to change these volumes while in silent mode.

The fix consists in modifying AudioService.setStreamVolumeInt() so that when a stream is affected by ringer mode
and we are in silent mode, only the saved volume value is modified, current value remaining to unchanged (0).