Bluetooth: Permit BT_SECURITY also for L2CAP raw sockets

Userspace pairing code can be simplified if it doesn't have to fall
back to using L2CAP_LM in the case of L2CAP raw sockets. This patch
allows the BT_SECURITY socket option to be used for these sockets.

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