Is it just me, or is /usr/src/include anemic?  It seems to lack everything
   starting with net.*, i.e., there is no /usr/src/include/net, /usr/src/include/
   netinet, et al. ...  Are these supposed to be somewhere other than
   /usr/src/include, for me to install them?

Is there some reason you didn't look at or use the provided Makefile,
which would explain all of this?