net: properly wrap context cancellation errors and return DNSErrors consistently
Fixes #71939
Change-Id: Id7cd720fcca2812ffca2b1b20fe923914422d994
GitHub-Last-Rev:
4671f338c91b5826c669fbd113c176e22f5020e5
GitHub-Pull-Request: golang/go#71941
Reviewed-on: https://go-review.googlesource.com/c/go/+/652275
Commit-Queue: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Damien Neil <dneil@google.com>