BUG/MINOR: mux-quic: Fix handling EOM after in qcs_http_rcv_buf()

BUG/MINOR: mux-quic: Fix handling EOM after in qcs_http_rcv_buf()

In qcs_http_rcv_buf() function, when the buffers cannot be swapped and
htx_xfer() function is called, the way the EOM flag is handled is buggy. The
htx_xfer() function is responsible to tranfer HTX flags from the QCS message
to the CS one. And when it is performed, HTX flags of the original message
are reset.

So, the following test on the EOM flag when the QCS message is empty is
never true. Because of this bug, QC_SF_EOI_SUSPENDED flag is never tested on
this code path and <fin> variable is not set to 1 as expected.

To fix the issue, we must test the EOM flag on the CS message.

This patch must be backported to 3.4.