Bluetooth: Use new hci_skb_pkt_* wrappers for core packet handling

The new hci_skb_pkt_* wrappers only help if they are used consistently
in the Bluetooth subsystem. So first convert the core packet handling.

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