workaround for intermittent failures of tcp_shutdown test on Windows

This gross hack avoids the tcp_shutdown test failure on Windows. It also fixes an abort during shutdown that we encountered in our internal product while using the ipc transport (our internal bug had lower repro, but wasn't as pathological as the tcp_shutdown test - still, it was the same issue).

I'm not suggesting that this be merged, but I'm hoping someone can provide some insight as to what is going on (e.g. what is a non NN_SOCK_SRC_EP doing here) and point towards a better fix.