mark potential peer as invalid after a few failed connection attempts

The client keeps track of potential peers by asking the peers it is currently connected to for their peers. Potential peers are kept in memory indefinitely. This leads to repeated failing connection attempts to stale peers.

Track the number of failed connection attempts per peer. If it crosses some threshold, don't attempt to connect to that peer. If the same peer gets announced again and some timeout has passed, reset the number of failed connection attempts and start connection attempts again.