testcases.py

* Fix longrtt

Wireshark now does not add "tls_handshake_type" attribute to a
retransmitted Initial packets which contain CRYPTO frame.  Instead, it
adds either "retransmission" or "overlap" attribute.  Consider these
attributes as a sign of retransmission of ClientHello.

See https://gitlab.com/wireshark/wireshark/-/issues/18696 for details.

* fixup! Fix longrtt