QUIC: fix Malformed Packet exception with small transport parameters

Since draft 27 the minimum transport parameter size can be smaller than
4 due to variable-length encoding. With ngtcp2-29-dsb.pcapng, the
active_connection_id_limit at the end covers only three bytes for
example. Even though the correct length is normally set later, the early
attempt to read four bytes resulted in an Malformed Packet exception.

Change-Id: I9ec6ec6c66ce7a993f2fcfdc987e35966dc809ac
Ping-Bug: 13881
Reviewed-on: https://code.wireshark.org/review/37483
Petri-Dish: Peter Wu <[email protected]>
Tested-by: Petri Dish Buildbot
Reviewed-by: Alexis La Goutte <[email protected]>

Author: Lekensteyn

epan/dissectors/packet-tls-utils.c

@@ -6867,7 +6867,7 @@ ssl_dissect_hnd_hello_ext_quic_transport_parameters(ssl_common_dissect_t *hf, tv
         guint64 value;
         guint32 len = 0;
 
-        parameter_tree = proto_tree_add_subtree(tree, tvb, offset, 4, hf->ett.hs_ext_quictp_parameter,
+        parameter_tree = proto_tree_add_subtree(tree, tvb, offset, 2, hf->ett.hs_ext_quictp_parameter,
                                                 NULL, "Parameter");
         /* TransportParameter ID and Length. */
         if (use_varint_encoding) {