Bluetooth: Fine tune audio gain for Absolute Volume case

Fine tune the audio gain for Bluetooth Absolute Volume.
Use 50%, 70% and 85% for lowest volume steps 1, 2 and 3.
Thus the volume change sounds smoother, more linear.
When remote end tune volume out of mute, we should also
tune the audio gain for the lowest volume steps.

Bug: 26694114
Change-Id: I298a334a4b40ddb87495fda1935349bfce8b0537
1 file changed