This changesets adds the possibility to fill a nl_cache with
the contents of the route cache. It also adds the possibility
to limit route caches to certain address families.
Adds all missing routing attributes and brings the routing
related code to a working state. In the process the API
was broken several times with the justification that nobody
is using this code yet.
The changes include new example code which is also a prototype
for how plain CLI tools could look like to control routes.
