bluetooth: Amend writeout to send more initial frames
requested to merge igor.v.kovalenko/pulseaudio:pr/issue-1424-bluetooth-write-more-frames-waiting-for-source into master
When bluetooth transport has both both sink and source, pulseaudio would synchronize writing out frames with reading frames from peer to make fair schedule of reads and writes. Pulseaudio allows two blocks of data to be sent to peer before synchronizing writes with reads just in case that peer implements similar write schedule.
It could happen that first blocks are still missed by peer, which would cause pulseaudio writes to stall waiting for first frames from peer.
Fix this by allowing more data frames out until data from peer is actually received.
Closes: #1424 (closed)