Fix audio gap observed issue when disc HID during A2DP Streaming

[Issue Description]
1. Pair and connect one A2DP headset and one HID mouse
2. A2DP streaming
3. Disconnect HID mouse
4. A2DP GAP observed while disconnecting HID mouse, GAP happen% > 50%
5. More info, did not hear GAP while reconnect the HID mouse so far.

[Root Cause]
When disconnect HID mouse, bluedroid will wait for polling thread to close,
which will block the callout and BTE task for some time especially during A2DP
streaming, which will leads to audio chopping and cause A2DP GAP in the streaming.

[Solution]
Set PTHREAD_CREATE_DETACHED property when create polling thread and don't wait for
the thread terminate when disconnect HID devices as the thread will stop it self after thread
loop ends

[More info]
This issue was first found from EEBU QA with W8887 and this should be one bug of bluedroid.

Change-Id: I612c812806e97f52f4ddb029688c846835ff2c5e
Signed-off-by: yangxx <yangxx@marvell.com>
a2dp: Reduce buffering of a2dp

Reduce the buffering of the a2dp audio stream
and remove the magic 200ms offset to latency.
The latency value seems to cause an issue with
Netflix app.

Bug 67611

Change-Id: I8c104c93380d6810bcca335e627329839095bc26