Fix a bug where the data that follows an HTTP upgrade response is lost

Related issue: #2179 and #2173

Motivation:

When a WebSocket server responds to a WebSocket handshake request with
its first WebSocket frame, it is sometimes swallowed by
HttpMessageDecoder.  This issue has been fixed by
4f6ccbbb78c88c82aa02c77fe7592709cfbf7922 in 4 and 5, but was not.

Modification:

Backport the UPGRADED state and the fix for #2173 to HttpMessageDecoder

Result:

The data sent by the server following an HTTP upgrade response is not
lost anymore.