libstagefright: LPAPlayer: Fix choppy playback on BT.

-Music playback on BT A2DP device is choppy/glitchy
-Decoder thread hogs the CPU this starves A2DP thread from data.
-Fix is to use small buffer(64k) only in the case of A2DP playback.

CRs-Fixed: 33353851
(cherry picked from commit e64bb36f81b22c93d3af156451b1236966c99ea4)

Conflicts:

	media/libstagefright/LPAPlayer.cpp

Change-Id: I2e9450a2be6f9e79e68d525d2119d33154d132b7