Bluetooth: Correct length calc in L2CAP conf rsp

cmd->len is in le format so convert it to host format before use.

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