We have seen in the past that there are peers in the IPFS DHT that let you connect to them but then refuse to speak any protocol. This was mainly due to resource manager killing the connection if limits were exceeded. We have seen that such peers are pushed to the edge of the DHT - meaning, they get already pruned from lower buckets. However, they won't get pruned from higher ones, because we only try to connect to them and not speak anything on that connection.

This change adds a ping message to the liveness check on routing table refreshes.

This reverts commit 16823c3.