i825xx: sni_82596: use eth_hw_addr_set()

netdev->dev_addr is now const, we can't write to it directly.
Copy scrambled mac address octects into an array then eth_hw_addr_set().

Fixes: adeef3e3

 ("net: constify netdev->dev_addr")
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Reviewed-by: Michal Kubiak <michal.kubiak@intel.com>
Link: https://lore.kernel.org/r/20230315134117.79511-1-tsbogend@alpha.franken.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>