Uncatched RejectedExecutionException on IOCP thread will crash the whole app after eventloop is stopped

[yyjdelete]

Unlike DotNetty, SpanNetty will throw RejectedExecutionException when try to submit to a eventloop after it's stopped. But unluckly it's not catched on callback of IOCP, then it will leak to threadpool, and crashes the whole app. (You can close all connected channel before close eventloop. But for connecting channel you can't do anything before it's timeout (if the dest is unavailable)) https://github.com/cuteant/SpanNetty/blob/472de8be9dcdbea9f70234096e3fb8274f3bf359/src/DotNetty.Transport/Channels/Sockets/AbstractSocketChannel.cs#L232-L286