Bluetooth: Change Sampling Frequency to 48 kHz

Change Default Sampling Frequency to 48 kHz by default to
match Audio Source.
CRs-fixed: 436686

Conflicts:
	audio_a2dp_hw/Android.mk
	btif/src/btif_media_task.c
	main/Android.mk

Change-Id: I73b6b2fe93df2dcede345e4063383aeab2fa05ae