support ipv6

[scareything]

Support ipv6 addresses, for both intercept and host service configurations.

[qrkourier]

I believed it already worked for host configurations. I haven't tested it since the tunneler SDK became available, but did test it successfully with early dayz Ziti when we had a need to host services that were IPv6 only.

[scareything]

Thanks for the note! I thought it might already work for host configurations (since we only pass the address to libuv when connecting to the hosting server), but I didn't know that we had already tried it.

I don't think we'll have much to do on the intercept side either, as we mostly use the lwip ip_addr_t type which can be either ip4 or ip6. I expect most of the work to be in the dns server, where we currently do not handle AAAA requests.

[scareything]

#869 was enough to get ipv6 intercept working on Linux. More work is needed for macOS (and probably Windows). At least for macOS the next obvious issues are:

• utun_add_route needs to parse out the prefix from the supplied route and pass it to the route command's -prefixlen option
• Adding ipv6 routes to the utun will not be possible until there is an ipv6 address assigned to the interface. Ideally this address would come from autoconfiguration / slaac, but it isn't immediately clear how to enable autoconf for utun devices.