[release-branch.go1.21] net: add GODEBUG=netedns0=0 to disable sending EDNS0 header
It reportedly breaks the DNS server on some modems.
For #6464
For #21160
For #44135
For #51127
For #51153
For #67925
Fixes #67933
Change-Id: I54a11906159f00246d08a54cc8be7327e9ebfd2c
Reviewed-on: https://go-review.googlesource.com/c/go/+/591995
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Damien Neil <dneil@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
(cherry picked from commit
ee4a42bd583b8594e97f1833c4b4c6e6428d9227)
Reviewed-on: https://go-review.googlesource.com/c/go/+/592235
Commit-Queue: Ian Lance Taylor <iant@google.com>