No support for IPv6

[jpatw]

The DNS tracer does not query IPv6 DNS servers.

The IPv6 addresses of the root nameservers are not used nor shown (all of them have IPv6).

Although the IPv6 addresses of intermediate nameservers are shown in the additional section, they are not queried. Requests are only sent to the legacy addresses. If a domain is IPv6-only then the trace fails entirely.

The tracer only queries for an A record, it does not allow setting any other types.