MINOR: quic: Do not use connection struct xprt_ctx too soon

In fact the xprt_ctx of the connection is first stored into quic_conn
struct as soon as it is initialized from qc_conn_alloc_ssl_ctx().
As quic_conn_init_timer() is run after this function, we can associate
the timer context of the timer to the one from the quic_conn struct.

src/xprt_quic.c

@@ -3687,7 +3687,7 @@ static int quic_conn_init_timer(struct quic_conn *qc)
 
 	qc->timer = TICK_ETERNITY;
 	qc->timer_task->process = process_timer;
-	qc->timer_task->context = qc->conn->xprt_ctx;
+	qc->timer_task->context = qc->xprt_ctx;
 
 	return 1;
 }