ACKs come with the source and destination address empty, this has been
clarified already. But there is something else: if the destination
address is empty but the source address is valid, it may be a way to
reach the PAN coordinator. Either the device receiving this frame is the
PAN coordinator itself and should process what it just received
(PACKET_HOST) or it is not and may, if supported, relay the packet as it
is targeted to another device in the network.

Right now we do not support relaying so the packet should be dropped in
the first place, but the stamping looks more accurate this way.
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Acked-by: Stefan Schmidt <stefan@datenfreihafen.org>
Acked-by: Alexander Aring <aahringo@redhat.com>
Link: https://lore.kernel.org/linux-wpan/20231128111655.507479-3-miquel.raynal@bootlin.com