I've made changes to fix some questionable code in netif_sun.c,
and I suspect this may fix netboot on machines where it broke.
The experimental version also has debug code in it.  The debug
code makes a lot of noise, so it's not turned on by default.
If this still breaks, let me know and I'll help debug it.

Get the file here:
ftp ftp.mc.com
cd /pub/gwr
binary
get netboot
bye