MINOR: quic: Missing QUIC encryption level for qc_build_pkt()

qc_build_pkt() has recently been modified to support any type of
supported frame at any encryption level (assuming that an encryption level does
not support any type of frame) but quic_tls_level_pkt_type()
prevented it from building application level packet type because it was written
only for the handshake.
This patch simply adds the remaining encryption level QUIC_TLS_ENC_LEVEL_APP
which must be supported by quic_tls_level_pkt_type().
diff --git a/include/haproxy/quic_tls.h b/include/haproxy/quic_tls.h
index d7ec049..d6d0e86 100644
--- a/include/haproxy/quic_tls.h
+++ b/include/haproxy/quic_tls.h
@@ -341,6 +341,8 @@
 		return QUIC_PACKET_TYPE_0RTT;
 	case QUIC_TLS_ENC_LEVEL_HANDSHAKE:
 		return QUIC_PACKET_TYPE_HANDSHAKE;
+	case QUIC_TLS_ENC_LEVEL_APP:
+		return QUIC_PACKET_TYPE_SHORT;
 	default:
 		return -1;
 	}