MemoryPool in SocketConnectionListener leaks after high load

[zackliu]

Describe the bug

I found lots of memory doesn't get gc after a very high load testing (More than 30000 websocket connections and concurrent sending message every 1 second on a 8 cores VM).
I got a dump after testing and found MemoryPool in SocketConnectionListener consumes a lot of memories.

To Reproduce

1. Make a large number of concurrent connections to a SignalR project and send quickly
2. End all connections

Further technical details

• ASP.NET Core version 3.1.5

[davidfowl]

Duplicate of #24958

I think we need to fix this now 😄