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.
Yes, we need an object to represent a single LRU table. But we don't need it right now. This code is tested, appears to be working, and is of comparable ugliness to the previous version.