net/http: Re-connect with upgraded HTTP2 connection fails to send Request.body [1.13 backport]

[gopherbot]

@networkimprov requested issue #32441 to be considered for backport to the next 1.13 minor release.

@gopherbot please backport, as Kubernetes is affected.

[andybons]

Approved as this is a serious enough regression with no suitable workaround.

[dmitshur]

@rsc This backport has been approved for 1.14 and 1.13. It applies cleanly to 1.14, but not 1.13. Since you authored the original CL, would you like to resolve the conflict (if it's possible to do so safely) and send a cherry-pick CL to release-branch.go1.13? Thank you.