fixes #495 warning in tcp_shutdown
fixes #495 warning in tcp_shutdown

reqshark/nanomsg,featherweight/ftw-kernel-nanomsg,yan97ao/nanomsg,snikulov/nanomsg,snikulov/nanomsg,thisco-de/nanomsg,reqshark/nanomsg,zerotacg/nanomsg,featherweight/ftw-kernel-nanomsg,yan97ao/nanomsg,imp/nanomsg,wirebirdlabs/featherweight-nanomsg,thisco-de/nanomsg,imp/nanomsg,JackDunaway/featherweight-nanomsg,imp/nanomsg,zerotacg/nanomsg,JackDunaway/featherweight-nanomsg,zerotacg/nanomsg,JackDunaway/featherweight-nanomsg,yan97ao/nanomsg,wirebirdlabs/featherweight-nanomsg,wirebirdlabs/featherweight-nanomsg,reqshark/nanomsg