MINOR: quic: use quic_conn as argument to traces

MINOR: quic: use quic_conn as argument to traces

Replace the connection instance for first argument of trace callback by
a quic_conn instance. The QUIC trace module is properly initialized with
the first argument refering to a quic_conn.

Replace every connection instances in TRACE_* macros invocation in
xprt-quic by its related quic_conn. In some case, the connection is
still used to access the quic_conn. It may cause some problem on the
future when the connection will be completly separated from the xprt
layer.

This commit is part of the rearchitecture of xprt-quic layers and the
separation between xprt and connection instances.