Bluetooth: Fix enhance audio streaming chopping issue

Bluetooth: Fix enhance audio streaming chopping issue

If BT controller's buffer is occupied by another profile such as
OPP or SPP, and it is blocked due to RF condition, A2DP packets
couldn't be sent properly. It causes the A2DP chopping issue.
It is because HCI buffer is limited but another tx requests
occupy it and audio streaming packet delay is occurred. So this
patch reserves some HCI buffer for A2DP to guarantee A2DP QoS
better.

Change-Id: I9e2e1fc718cfa6b65dcd0e3aa4439ccce4da99a2
Signed-off-by: Seungyoun Ju <sy39.ju@samsung.com>
Signed-off-by: Hyuk Lee <hyuk0512.lee@samsung.com>