* swarm/network: fix skipped tests related to suggestPeer

* swarm/network: rename depth to radius

* swarm/network: uncomment assertHealth and improve comments

* swarm/network: remove commented code

* swarm/network: kademlia suggestPeer algo correction

* swarm/network: kademlia suggest peer

 * simplify suggest Peer code
 * improve peer suggestion algo
 * add comments
 * kademlia testing improvements
   * assertHealth -> checkHealth (test helper)
   * testSuggestPeer -> checkSuggestPeer (test helper)
   * remove testSuggestPeerBug and TestKademliaCase

* swarm/network: kademlia suggestPeer cleanup, improved comments

* swarm/network: minor comment, discovery test default arg