Bluetooth: Add Bluetooth socket voice option

This patch extends the current Bluetooth socket options with BT_VOICE.
This is intended to choose voice data type at runtime. It only applies
to SCO sockets. Incoming connections shall be setup during deferred
setup. Outgoing connections shall be setup before connect(). The desired
setting is stored in the SCO socket info. This patch declares needed
members, modifies getsockopt() and setsockopt().

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