[avalanche] Request more node addresses upon receipt of a dangling proof

Summary: A proof that has been dropped because of no associated node will not be registered again until a node requests it. But if we get that dangling proof again, it's a hint that we might be missing the node, so trigger a request in this case.

Test Plan:

ninja all check-all

Reviewers: #bitcoin_abc, sdulfari

Reviewed By: #bitcoin_abc, sdulfari

Differential Revision: https://reviews.bitcoinabc.org/D11792