better/proper duplicate route handling

[KanjiMonster]

Currently, BISDN Linux does not handle duplicate routes very well. This is partially due to libnl not properly treating multiple routes with identical metric as a single route that changes its interface, and partially due to baseboxd not being prepared for multiple routes at all.

To better support this, we basically need to fix various places.

1. baseboxd needs to learn to handle multiple routes with different priorities for the same destination, and keep the route with the highest priority (lowest metric) enabled. This may require keeping track of routes within baseboxd to properly update the ASIC configuration.
2. libnl needs to learn treat multiple routes for the same destination as multiple routes, IF they are multiple routes in the kernel. This is non trivial, and may not even be achievable, depending on how detailed the information is that is shared by the kernel via netlink.