I've slightly reworked the  Ultrix compatiblity code.

Several bug in handling Ultrix socket ioctls have been fixed.  Ultrix
compatibility mode now works with the Ultrix /etc/ifconfig, well
enough for the Ultrix ifconfig command to to bring interfaces up and
down and add routes.

Ultrix binaries that use the IPmulticast patches (e.g., the LBL
toolsuite) also work in  Ultrix compatibility mode.

The full X11R6.1 user-level suite now also works, including xdm (but
of course the Xserver, unless you have an Xserver from Ultrix 4.1 or
older).  I'd recommend installing the X116.3 snapshot anyway, but this
may be to anyone who needs to coexist with an installed base of Ultrix
machines.

An ECOFF-format netbsd kernel may even boot and go multi-user if
dropped into an Ultrix root filesystem, but I haven't actually tried
it myself.  I'd be very interested to hear from anyone who does :).