MEDIUM: mux-h2: Don't expect data from server as long as request is unfinished

MEDIUM: mux-h2: Don't expect data from server as long as request is unfinished

As for the H1 stream, the H2 stream now states it does not expect data from
the server as long as the request is unfinished. The aim is the same. We
must be sure to not trigger a read timeout on server side if the client is
still uploading data.

From the moment the end of the request is received and forwarded to upper
layer, the H2 stream reports it expects to receive data from the opposite
endpoint. This re-enables read timeout on the server side.