net/faraday: Disallow using reversed MAC address from hardware

net/faraday: Disallow using reversed MAC address from hardware

The initial MAC address is retrieved from hardware if it's not
provided by device-tree. The reserved MAC address from hardware
will be used if non-reserved MAC address is invalid. It will
cause mismatched MAC address seen by hardware and software.

This disallows using the reserved hardware MAC address to avoid
the mismatched MAC address seen by hardware and software.

Fixes: cccb48007a79 ("net/faraday: Read MAC address from chip")
Suggested-by: David Laight <David.Laight@ACULAB.COM>
Suggested-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>