MINOR: quic: As server, skip 0-RTT packet number space

This is true only when we are building packets. A QUIC server never
sends 0-RTT packets. So let't skip the associated TLS encryption level.
diff --git a/src/xprt_quic.c b/src/xprt_quic.c
index 07dcbd7..4d0f752 100644
--- a/src/xprt_quic.c
+++ b/src/xprt_quic.c
@@ -3200,7 +3200,10 @@
 
 	if (!qr)
 		qr = MT_LIST_POP(qc->tx.qring_list, typeof(qr), mt_list);
-	if (!quic_get_tls_enc_levels(&tel, &next_tel, st, zero_rtt))
+	/* A listener does not send any O-RTT packet. O-RTT packet number space must not
+	 * be considered.
+	 */
+	if (!quic_get_tls_enc_levels(&tel, &next_tel, st, 0))
 		goto err;
 	ret = qc_prep_pkts(qc, qr, tel, next_tel);
 	if (ret == -1)