bluedroid: Fix build with gcc 4.8+

Use -Wno-error=unused-parameter with gcc >= 4.8

Change-Id: Id7299c8f0a1e2dd683647d49225342ebfa0a8dcf
Update btif_media_task.c

Change middle quality to high quality for A2DP streaming to solve the issue of disortion in higher frequencies of music playback.  Refer to Android Google code issue 39632.