old (before ARP changes) <netinet/if_ether.h>, intended for temporary use.
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.
closely after the build process used by NetBSD/alpha's boot code.