Restore permission check for mic muting

The implementation for AudioManager.setMicrophoneMute() used to
 call directly into AudioSystem which called directly into
 AudioFlinger and the mediaserver process, where the check for
 the MODIFY_AUDIO_SETTINGS is performed.
A regression was introduced by Ib32138bcc256cfbac4fe21a090d5ba34f5c641fc
 which calls first into AudioService which runs in system_process
 before calling into AudioSystem, which granted the permission.
This CL adds a permission check in this code path when calling
 AudioService.

Bug 17259652

Change-Id: I4ac5269262eb90df80ee81db6ec3d96977ee53be