nl_l3: only route l3 neighs if we have a route for them

[KanjiMonster]

Make sure we do not add host entries for l3 neighs for which we do not have a route until we a route gets added, and drop the host entries again when the route gets removed.

To do this, we need to start keeping track of all l3 neighs we currently handle. To make this easy, use set, and reuse the nh_stub to store the neighbor information.

To allow nh_stub to be used in a set, we need to make it comparable, so implement the < operator for it.

Using this we can then determine the routability of a l3 neigh we add by asking the kernel for the route to it, then checking if it has a nexthop that exist on one of our interfaces.

Only if this is true, add a host route for it and add it to the set of routed l3 neighbours, in all other cases add it to the set of unrouted l3 neighbours.

Then when adding a route, add all currently unrouted l3 neighbors matching this route, and conversely, when removing a route remove all matching l3 neighbors that are currently routed.

Fixes l3 neighbours learned on an additional on-link staying reachable after removing the on-link route.

Signed-off-by: Jonas Gorski jonas.gorski@bisdn.de

How Has This Been Tested?

Using the commands from https://github.com/bisdn/basebox/issues/364 and verified that no host entries get added without a on-link route, and the host entry appearing and vanashing when adding and removing the on-link route.

Running a pipeline on ag5648 to check for regressions.

[KanjiMonster]

IPv6 link-local will need some special handling, will fix that tomorrow.

[KanjiMonster]

Fixed IPv6 by ignoring IPv6 LL addresses; these should be unroutable anyway.