net/eth/ibmveth: Fixup retrieval of MAC address

net/eth/ibmveth: Fixup retrieval of MAC address

commit 13f85203e1060da83d9ec1c1c5a63343eaab8de4 upstream.

Some ancient pHyp versions used to create a 8 bytes local-mac-address
property in the device-tree instead of a 6 bytes one for veth.

The Linux driver code to deal with that is an insane hack which also
happens to break with some choices of MAC addresses in qemu by testing
for a bit in the address rather than just looking at the size of the
property.

Sanitize this by doing the latter instead.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>