Bluetooth: Fix L2CAP channel closing for LE connections

Sending of the L2CAP Disconnect request should also be performed for LE
based channels. The proper thing to do is therefore to look at whether
there's a PSM specified for the channel instead of looking at the link
type.

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