The seeder was intended to fetch address lists of nodes once a day:
https://github.com/sipa/bitcoin-seeder/commit/966d040f8d976bc824821c5b2bb778363b5128fa
However, ourLastSuccess is updated each time a node is successfully
connected, which can be up to every 15 minutes. This effectively means
that address lists are only fetched when a node has been down for a day,
which means the seeder only queries address lists from new or unreliable
nodes.
To fix this, we add the new timestamp lastAddressRequest to the
database, which means the format is now version 5. This timestamp is
used to keep track of when we last send a getaddr / getheaders
request to a node.
This is a backport of bchn#1042
Depends on D16465
This fix is important if we want the improvement from D16465 to actually apply to nodes that are already in the database. Without the fix, the existing BCH and BSV nodes that are in the db will not get removed because the check never runs.