'net' module: tests and fixes

So far this updates #308 with a very basic test suite, and fixes IPv4 and/or IPv6 address detection.
Ah, interesting. But isn't `aucInactivity` a global setting? So maybe we eventually need both: this per-socket watchdog, but also add logic that looks at the max timeout across all TCPSocket instances and updates `aucInactivity` to that.