logparse.pl: add verbose dumping for transport protocol.

This includes picking apart the various asymmetric crypto formats
(public keys, signatures, elliptic-curve point encodings) as far as
possible, but since the verbose decoder system in logparse.pl
currently has to work without benefit of statefulness, it's not always
possible - some of the ECC formats depend for their decoding on
everyone remembering _which_ ECC protocol was negotiated by the
KEXINITs.