* Keep detailed stats on the peer testing, publishing the results in the
      netDb.
    * Don't overwrite the status with 'unknown' unless we haven't had a valid
      status in a while.
    * Make sure to avoid shitlisted peers for peer testing.
    * When we get an unknown result to a peer test, try again soon afterwards.
    * When a peer tells us that our address is different from what we expect,
      if we've done a recent peer test with a result of OK, fire off a peer
      test to make sure our IP/port is still valid.  If our test is old or the
      result was not OK, accept their suggestion, but queue up a peer test for
      later.
    * Don't try to do a netDb store to a shitlisted peer, and adjust the way
      we monitor netDb store progress (to clear up the high netDb.storePeers
      stat)