Refactor StaleBestPathRoute
This removes the dependency on RIBSupport by forcing users to provide
proper lists. Since there are only two users, we can create specialized
instances, co-located with them, so that we do not have to cross through
SPI/implementation boundaries.
This allows saves quite a bit of memory in non-addpath case and also
improves code AddPathAbstractRouteEntry isolation, as we no longer
leak List<Long> all over the place.
Change-Id: I48b91d15df738095812736dfdeaa71d88b30598b
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>