BUG/MEDIUM: mux-quic: fix EOI for request without payload

BUG/MEDIUM: mux-quic: fix EOI for request without payload

When a full message is received for a stream, MUX is responsible to set
EOI flag. This was done through rcv_buf stream callback by checking if
QCS HTX buffer contained the EOM flag.

This is not correct for HTTP without body. In this case, QCS HTX buffer
is never used. Only a local HTX buffer is used to transfer headers just
as stream endpoint is created. As such, EOI is never transmitted to the
upper layer.

If the transfer occur without any issue, this does not seem to cause any
problem. However, in case the transfer is aborted, the stream is never
released which cause a memory leak and prevent the process soft-stop.

To fix this, also check if EOM is put by application layer during
headers conversion. If true, this is transferred through a new argument
to qc_attach_sc() MUX function which is responsible to set the EOI flag.

This issue was reproduced using h2load with hundred of connections.
h2load is interrupted with a SIGINT which causes streams to never be
closed on haproxy side.

This should be backported up to 2.6.