DNS proxy listen on IPv6 in addition to IPv4 localhost

[ondruska]

I have just found out that on Windows 10 cloudflared DNS proxy listens on IPv4 localhost only (UDP port 53). I have not found documentation option to include listening on IPv6 localhost as well and hence I am unable to force interface with IPv6 to use cloudlared DNS proxy.
Another side effect is that if I set IPv6 preferred DNS to ::1 Windows and IPv4 DNS server to 127.0.0.1 resolution fails as Windows tries to use ::1 only--but this could be my Windows issue.

[moderation]

@ondruska It's annoying that it isn't documented but the solution is described at #73 (comment). I'll raise a doco PR and see if it is accepted.