MINOR: mux-quic: adjust Rx data consumption API

MINOR: mux-quic: adjust Rx data consumption API

HTTP/3 data are converted into HTX via qcc_decode_qcs() function. On
completion, these data are removed from QCS Rx buffer via qcs_consume().

This patch adjust qcs_consume() API with several changes. Firstly, the
Rx buffer instance to operate on must now be specified as a new argument
to the function. Secondly, buffer liberation when all data were removed
from qcs_consume() is extracted up to qcc_decode_qcs() caller.

No functional change with this patch. The objective is to have an API
which can be better adapted to multiple Rx buffers per QCS instance.