ipdb: incapsulate nla_fields into the Interface class
iproute: break too complext statement in get_routes

To ease debug
iproute: new route interface, +set command

Though compatible with the old one, it accepts now raw requests like
link routine does. Also, 'set' route from now on is possible too.
[UNSTABLE] ipdb: routing infrastructure, alpha version

Obs! This commit is NOT stable and it HAS issues. Refer to the code
and run tests to reproduce.