Bluetooth: Implement deferred sco socket setup

In order to authenticate and configure an incoming SCO connection, the
BT_DEFER_SETUP option was added. This option is intended to defer reply
to Connect Request on SCO sockets.
When a connection is requested, the listening socket is unblocked but
the effective connection setup happens only on first recv. Any send
between accept and recv fails with -ENOTCONN.

Signed-off-by: Frédéric Dalleau <frederic.dalleau@linux.intel.com>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>