Changes to `proxy_set_header Connection` needed.

[SX86]

Issue: I found that using proxy_set_header Connection "upgrade"; would cause the following error on some reverse proxy'd web apps.

Microsoft.AspNetCore.Server.Kestrel.Core.BadHttpRequestException: Requests with 'Connection: Upgrade' cannot have content in the request body.

Suggested change: Use proxy_set_header Connection $http_connection; instead.

So far, the results look similar, if not the same same, and I am no longer getting the above error.

Source of the fix: https://github.com/aspnet/KestrelHttpServer/issues/1263

[orobardet]

Will proxy_set_header Connection $connection_upgrade; works too? As this is the default value set for Connection header in latest DSM to handle Websocket, I would prefer to change to $connection_upgrade if it works the same as $http_connection for your need.

[SX86]

I would have to test and see. I'm not even sure how the whole thing works, I just know that this simple change fixed an error I was getting for one particular web app.

Let me know if you need me to test it, or for me to give you more context on that specific issue.