Motivation
A GOAWAY frame (or any other HTTP/2 frame) should not be sent before the
connection preface. Clients that immediately close the channel may
currently attempt to send a GOAWAY frame before the connection preface,
resulting in servers receiving a seemingly-corrupt connection preface.
Modifications
* Ensure that the preface has been sent before attempting to
automatically send a GOAWAY frame as part of channel shutdown logic
* Add unit test that only passes with new behavior
Result
Fixes https://github.com/netty/netty/issues/11026
Co-authored-by: Bennett Lynch <Bennett-Lynch@users.noreply.github.com>