ISPN-3375 Improve default JGroups configuration

* Make TP.max_bundle_size and FRAG2.frag_size the same, 30k
  (As datagrams larger than 32k are not always supported.)
* Enable the INTERNAL thread pool
* Increase the UFC/MFC.max_credits
* Configure FD_ALL.interval so that a node is suspected only after 5 missed
  heartbeats