Hammerhead - Change headset mic gain for voice call

Decrease headset mic gain by 8dB for
voice call

Bug: 11660005

Change-Id: Icc9d06bc426727e3fc1834a9813170aca8584f52
Signed-off-by: MURA Stefano [STELIX PippoX3] <ssspinni@gmail.com>