MINOR: mux-quic: properly report end-of-stream on recv

MINOR: mux-quic: properly report end-of-stream on recv

MUX is responsible to put EOS on stream when read channel is closed.
This happens if underlying connection is closed or a RESET_STREAM is
received. FIN STREAM is ignored in this case.

For connection closure, simply check for CO_FL_SOCK_RD_SH.

For RESET_STREAM reception, a new flag QC_CF_RECV_RESET has been
introduced. It is set when RESET_STREAM is received, unless we already
received all data. This is conform to QUIC RFC which allows to ignore a
RESET_STREAM in this case. During RESET_STREAM processing, input buffer
is emptied so EOS can be reported right away on recv_buf operation.

This should be backported up to 2.7.