Bluetooth: hci_intel: Give priority to LPM packets

Change the way to insert LPM packets into the txq.
Use skb_queue_head instead of skb_queue_tail to always prioritise LPM
packets over potential tx queue content.

Signed-off-by: Loic Poulain <loic.poulain@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>