[DGD] Prep for FTP daemon

[Shentino]

I'm in the middle of writing a passive FTP daemon, but ran across a
technical problem.

How does the mudlib find out the IP address of the server it's running
on?  (required in the reply to PASV)

I'll probably need a C helper outside of DGD to do the lookup so I can
stash a file in System or something.

What do I do to find out my own IP address?  I'm pretty clueless in
the C networking department.