i386/105708: em driver failed to initialize on thinkpad X60

[nonomura at nifty.com]

> I doubt it.  hw.pci.allow_unsupported_io_range never existed in RELENG_6,
> and now also doesn't exist in HEAD.  I think you're just lucky as Gleb;
> sometimes it just boots.  :-)
You are right.

I've tried to remove  hw.pci.allow_unsupported_io_range="1",
then it still works.

I can not say when the issue happens, but looks like this happens
when ethernet cable is not connected.