Comment 1 for bug 1299374

The code uses the broadcast address (which is optional), not the interface's IP address (which is required), to define the network's address. Why!? I see no comment, and I'm fairly sure the IP address wasn't added later.

To make things even more confusing, model validation does require that the interface's IP address be in the same network. So there is no situation where the broadcast address might have information that we need and can't get from the IP address. I think we can just derive the full network spec from IP address and netmask, and make the broadcast address optional.