Split opennet routing table into short links and long links (refactored)

This is similar to split-opennet-routing-table-original, which is better tested, but cleaned up history and with some minor opennet refactoring included. It does appear to work.
Not that function, no. It might be possible to refactor to make it more general; the plan was to allow other kinds of e.g. anonymous setup, and we might still need that e.g. for darknet invites.