8.1.1 High ERR_CLIENT_ABORTs

[masaori335]

We observed high ERR_CLIENT_ABORTs on 8.1.1. We haven't seen this issue prior to this version.

So far, dc7b869 is the suspicious commit, but it's unclear how it's making the issue. Because we're not using proxy.config.http.attach_server_session_to_client (= 0 as default).
It turned out dc7b869 is unrelated.

[masaori335]

I still don't have repros for this, but it seems this issue comes from 8eb6826 and related to the following redirects.
Hopefully, #7401 fix this issue too. I'll try the patch after the new year off.

[masaori335]

We've started a trial of the #7401 fix. So far, it seems like #7401 fixed this issue too.