AudioService: setMasterMute protected by MODIFY_AUDIO_ROUTING

Require MODIFY_AUDIO_ROUTING system permission to exercise
hidden (non-SDK, non-SystemApi) method setMasterMute

Bug: 141622311
Test: see bug for POC app
Change-Id: I4ee93276daa1285c55c4c838e2b43833135d76f6
2 files changed