Clean up the name space here a bit.
Add a `busname' element to struct ofprobe (now struct ofbus_attach_args), and
check against it.
Nuke `ofroot'.
Rename the `openfirm' attribute to `ofbus'.
Some of the stuff (e.g., rarpd, bootpd, dhcpd etc., libsa) still will
only support Ethernet. Tcpdump itself should be ok, but libpcap needs
lot of work.
For the detailed change history, look at the commit log entries for
the is-newarp branch.
