Connection manifest will drop connections after 24 hours

[ghjm]

The connection manifest writes connections to disk so that a node can remember, after restart, what connections it used to have, even if they happen to be down right now. This allows it to buffer messages for a connection that might come back up soon.

As far as I can see, the connection manifest's update method only gets called when a node connects or disconnects. So on a stable network where nodes have remained connected for more than 24 hours, the watch_expire process will drop nodes from the manifest, even though they are still active.

[matburt]

This probably just needs a test to see if this connection is active and if it is it can skip over it. connects/disconnects will update this time.

[ghjm]

It's not good enough for connects/disconnects to update the time. We hope these connections will be up and stable for weeks, months or years at a time. We probably need to update on traffic, or have a background task that resets the time periodically as long as the connection is still up.