machines with old firmware which doesn't pass it in the boot device
can work. Assume that if the ethernet address isn't passed in, it
uses the old (dain-bramaged) 'read' interface works on my 3000/300LX.
(1) the if_prom code needs to be cleaned up quite a bit
(right now it hard-codes client's ethernet address), and
(2) much of this code (esp: getsecs.c, netboot.c, newvers.sh,
rpcc.S) should be shared with other Alpha boot blocks,
and dev_net.[ch] should maybe go in libsa proper.