Bluetooth: Move and rename hci_conn_accept

Since this function is only used by sco, move it from hci_event.c to
sco.c and rename to sco_conn_defer_accept. Make it static.

Signed-off-by: Frédéric Dalleau <frederic.dalleau@linux.intel.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>