A2DP: Lowering maximum PCM frame limit to avoid audio breaks

Some car kits (notably Renesas car kits used in Nissan/Infiniti models)
will throttle incoming A2DP frames if too many frames are sent at once.
This patch lowers the maximum number of frames sent per tick to not
overwhelm the remote device.

Bug: 17880920
Change-Id: I7bfbba625405c96159d1c94eebd8dc498f100daa