64000 routes or bust!

[dtaht]

In part I'm trying to abuse the new make-wifi-fast aqm code. But getting babel up to a city scale
has always been a goal of mine. The new unicast stuff (I hope) will do route transfers over unicast,
which means that if there are no listeners on a wifi bridge, we won't see the packets go. That should
be an enormous improvement in itself.

There are multiple other places that can be sped up. Routing updates can be made atomic (halving
their cost). We can get better about doing route retractions on a denser mesh and install a better route at the outset #5 . We can start announcing routes on a longer interval (supported by the protocol, probably,
but not the current babeld code).