Under heavy PCI bus load, ports of the DFE-580TX 4-ethernet port board stop
working, with currently no other cure than a powercycle.  Here is a tested
fix.  By the way, I also fixed some references and attribution.
Signed-off-by: Philippe De Muyter <phdm@macqel.be>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>