Bluetooth: Use GFP_KERNEL when cloning SKB in a workqueue

There is no need to use GFP_ATOMIC with skb_clone() when the code is
executed in a workqueue.

Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Acked-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>