WindowsParser support for _default_interface

[PaluMacil]

_default_interface throws an attribute exception on Windows. I'm only a hobbyist in Python (work is C#) so I could be missing something, but it looks like this is only implemented for Unix. It also looks fairly easy to add. If I'm not misunderstanding anything, I'd like to make a pull request. I'm using your library for observing Raspberry Pis I'll register to my home network, but I figure I might as well use Windows to test so that I can make the library better for cross-compat cases.