[Bluetooth] Move pending packets from RFCOMM socket to TTY

When an incoming RFCOMM socket connection gets converted into a TTY,
it can happen that packets are lost. This mainly happens with the
Handsfree profile where the remote side starts sending data right
away. The problem is that these packets are in the socket receive
queue. So when creating the TTY make sure to copy all pending packets
from the socket receive queue to a private queue inside the TTY.

To make this actually work, the flow control on the newly created TTY
will be disabled and only enabled again when the TTY is opened by an
application. And right before that, the pending packets will be put
into the TTY flip buffer.

Signed-off-by: Denis Kenzior <denis.kenzior@trolltech.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>