Bluetooth: Fix BT_SECURITY socket option for fixed channels (ATT)

The BT_SECURITY option should also be allowed for fixed channels, so
punch the appropriate hole for it when checking for the channel type.
The main user of fixed CID user space sockets is right now ATT (which is
broken without this patch).

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>