HPCC-11025 - Fix various MP close socket issues

Fix:
1) Spot non-MP clients connecting to the MP port early and ignore.
2) IpAddress::setNetAddress - set 'null' ip if null IPv4 provided.
3) Ignore InterCommunicator close sockets as exceptions unless
specifically listening to socket closed.
4) Ingore Communicator close socket exceptions unless part
internal to group communicator is based on.
5) Ensure close socket exception on Thor watchdog recycles Thor.

Signed-off-by: Jake Smith <jake.smith@lexisnexis.com>
HPCC-11025 - changes after review
Merge pull request #5537 from jakesmith/hpcc-11025

HPCC-11025 - Fix various MP close socket issues

Reviewed-By: Gavin Halliday <gavin.halliday@lexisnexis.com>
Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>