A2DP HAL: Update maximum Audio buffer size

Due to Audio buffer equal to socket buffer size observed A2dp
Chopiness randomly because of socket write blocking for long
time. Update maximum Audio buffer size to 3072 bytes.

CRs-Fixed: 648712

Conflicts:
	audio_a2dp_hw/audio_a2dp_hw.c

Change-Id: I506081e906a7539aff27895368b30171bea871c3