MAC address in the EEPROM, and we need to get it from OpenFirmware.
This isn't very pretty but time is lacking to do this in a better
way this near 5.2-RELEASE. This is a RELENG_5_2 candidate.
Original version by: Marius Strobl <marius@alchemy.franken.de>
Tested by: Pete Bentley <pete@sorted.org>
Reviewed by: jake