Allow to disable sends or receives on a socket using shutdown(2) by interpreting NULL 'data' argument passed to proto_common_send() or proto_common_recv() as a will to do so.
Allow to disable sends or receives on a socket using shutdown(2) by
interpreting NULL 'data' argument passed to proto_common_send() or
proto_common_recv() as a will to do so.

MFC after:	1 month

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase