AudioService: modify unmute on device plug behavior

Only unmute STREAM_MUSIC on audio device connection when the muting
doesn't come from the Zen mode's muted streams.

Bug: 128161896
Test: enter Zen mode other than NO_INTERRUPT with no media playback,
   plug headset and verify audio is muted when playing media.

Change-Id: I1ccd0ea35d8a84ec400db3d60ba509183e1abded