net: consistently return DNSError on lookup failure
Previously if we failed because the context timed out or was canceled,
we returned errCanceled or errTimeout.
Fixes #39178
Change-Id: I11bd7ebfaa7e5775fb05dfbb6b67f8307c8d8697
Reviewed-on: https://go-review.googlesource.com/c/go/+/353400
Trust: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Go Bot <gobot@golang.org> Reviewed-by: Damien Neil <dneil@google.com>