Bluetooth: Host: add pub_key_hci_disrupted function

Add bt_pub_key_hci_disrupted function for when hci is disrupted during
a pub key hci command, to clear callbacks and BT_DEV_PUB_KEY_BUSY flag.

Call this from bt_disable for the case bt_disable disrupts the pub key
hci command.

Signed-off-by: Sean Madigan <sean.madigan@nordicsemi.no>