H2C upgrades should be ineligible for flow control
Motivation:
When the h2c upgrade request is too big, the Http2FrameCodec complains
it's too big for flow control reasons, even though it's ineligible for
flow control.
Modifications:
Specially mark upgrade streams and make Http2FrameCodec know not to try
to flow control on those streams.
Result:
Servers won't barf when they receive an upgrade request with a fat
payload.
[Fixes#7280]
0cac1a6c8c