P2p: count connections without activity; use the counter when calculating next connection attempt time, to make it progressively bigger as the counter grows.

[ImplOfAnImpl]

If an outgoing connection gets closed without peer having done any activity (which means it didn't sent us any message except for WillDisconnect), peer address's connections_without_activity_count will be incremented. This counter is then used in AddressData::next_connect_time the same way as the already existing fail_count is - the bigger the counter, the longer the time before the next connection is attempted.

I.e. if the node gets banned by a peer (which doesn't necessarily mean that there is something wrong with the node, e.g. the fork detection script uses banning to prevent connecting to the same nodes every time), the current behavior is that the node will relentlessly try connecting to the peer every 10 seconds or so. The new behavior is that the delay before the next connection attempt will gradually increase as the counter grows, up to the maximum (which is currently 1h for non-
reserved peers).

Note:

• Unlike fail_count, connections_without_activity_count won't cause the peer address to become Unreachable eventually.
• Like fail_count, connections_without_activity_count is not stored in the peer db on disk; it only exists in memory and will be zero again when the node is restarted.