In the probe routines check the mainbus attach args mb_iobase field
to verify that the iobase did not default as an iobase address needs
to be specifically specified.
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.