net/http/httputil: remove all fields in Connection header
In the reverseproxy, replace use (Header).Get, which returns only one value
of a multiple value header, with using the Header map directly. Also fixes
corresponding tests which hid the bug, and adds more tests.
Fixes #30303
Change-Id: Ic9094b5983043460697748759f6dfd95fc111db7
GitHub-Last-Rev:
b41038143f602d4286cb46c542d40de02e6e639d
GitHub-Pull-Request: golang/go#30687
Reviewed-on: https://go-review.googlesource.com/c/go/+/166298
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>