Update the DHT like trackers in small swarms

[mcaspi]

The DHT and the trackers don't function the same when it comes to updating after a stop or a pause. They used to function the same way if I remember correctly. I guess that the change was made in order to prevent a big amount of connection attempts to peers from the trackers and the DHT at the same time. But if the swarm is small I don't see a reason why not updating the DHT after a pause or a stop in the same way that trackers are updated. My suggestion in this case is to update the DHT based on the number of peers in a swarm.