Add support for IPv6 flags

Ocelot does not allow anyone with an IPv6 address to torrent from it. The implementation should follow [BEP 07](http://www.bittorrent.org/beps/bep_0007.html). [Radiance](https://github.com/Empornium/Radiance) can also be used as a reference for how to do it.

A partial implementation lives in the ipv6 branch.