BUG/MINOR: h3: handle unknown frame type on request stream as specified

BUG/MINOR: h3: handle unknown frame type on request stream as specified

HTTP/3 specification allows the ability to define extra frame types. An
implementation must silently ignored unknown frame types.

Prior to this patch, haproxy stack completely discards an unknown frame.
However, on a request stream, if this acts as the last stream frame, it
would lead to a missing HTX EOM before the stream is closed on timeout.

Now, an HTX EOM is properly reported to the upper layer, which ensures
the request can successfully be achieved. A reset is emitted though if
no headers were previously received as in this case the HTTP request is
incomplete.

This must be backported up to 2.6.