Ensure that the upstream is always queried, so that if upstream is going
to NXDOMAIN natc will also return NXDOMAIN rather than returning address
allocations.
At this time both IPv4 and IPv6 are still returned if upstream has a
result, regardless of upstream support - this is ~ok as we're proxying.
Rewrite the tests to be once again slightly closer to integration tests,
but they're still very rough and in need of a refactor.
Further refactors are probably needed implementation side too, as this
removed rather than added units.
Updates #15367
Signed-off-by: James Tucker <james@tailscale.com>
025fe72448