The resolver still only supports a single upstream config, and
ipn/wgengine still have to split up the DNS config, but this moves
closer to unifying the DNS configs.
As a handy side-effect of the refactor, IPv6 MagicDNS records exist
now.
Signed-off-by: David Anderson <danderson@tailscale.com>
They're only used internally and in tests, and have surprising
semantics in that they only resolve MagicDNS names, not upstream
resolver queries.
Signed-off-by: David Anderson <danderson@tailscale.com>
