Add a set of D defines based on the contents of socket.h

[gnn]

Summary

Pulls in the various SO_, AF_, and PF_ defines for use in D scripts

[markj]

This should go in cddl/lib/libdtrace so that it gets included automatically like the rest of the libraries. Otherwise it seems ok to me.

We really need a way to avoid duplicating these definitions. I think illumos has some build-time sed script that substitutes the values from the corresponding header, but I haven't looked at it closely.

[markj]

Also missing a makefile update.

[gnn]

It bugs me to have new, BSD licensed, code in the cddl directory but I'm OK with this being there for now. And, yes, we need an automagic way to generate these.