BUG/MINOR: hq-interop: adjust parsing/encoding on backend side

BUG/MINOR: hq-interop: adjust parsing/encoding on backend side

HTTP/0.9 is available on top of QUIC. This protocol is reserved for
internal use, mostly interop purpose.

This patch adjusts HTTP/0.9 layer with the following changes :
* version is not emitted anymore on the status line. This is performed
  as some servers does not parse it correctly.
* status line is set explicitely on HTX status-line. This ensures the
  correct HTTP status code is reported to the upper stream layer.

This does not need to be backported.