Bluetooth: Don't check encryption for L2CAP raw sockets

For L2CAP sockets with medium and high security requirement a missing
encryption will enforce the closing of the link. For the L2CAP raw
sockets this is not needed, so skip that check.

This fixes a crash when pairing Bluetooth 2.0 (and earlier) devices
since the L2CAP state machine got confused and then locked up the whole
system.

Signed-off-by: Marcel Holtmann <marcel@holtmann.org>