MEDIUM: quic: Add connection as argument when qc_new_conn() is called

MEDIUM: quic: Add connection as argument when qc_new_conn() is called

This patch reverts the commit efe60745b ("MINOR: quic: remove connection arg
from qc_new_conn()"). The connection will be mandatory when the QUIC
connection is created on backend side to fix an issue when we try to reuse a
TLS session.

So, the connection is again an argument of qc_new_conn(), the 4th
argument. It is NULL for frontend QUIC connections but there is no special
check on it.