Phantom "ip0" interface on SunOS 3.x

[dupuy at cs.columbia.edu]

Using the SIOCGCONF ioctl to get the interfaces on a Sun running 3.x
returns a phantom third interface, "ip0", which can be queried with the
ifconfig program:

$ ifconfig ip0
ip0: 0.0.0.0 flags=0<>

This seems to be created in the ip_init() routine in ip_input.c.  Does
anybody have any idea why?  Neither SunOS 4.0 or 4.3 bsd do this.  Is it a
4.2 relic?

@alex