MINOR: quic-be: Correct Version Information transp. param encoding

MINOR: quic-be: Correct Version Information transp. param encoding

According to the RFC, a QUIC client must encode the QUIC version it supports
into the "Available Versions" of "Version Information" transport parameter
order by descending preference.

This is done defining <quic_version_2> and <quic_version_draft_29> new variables
pointers to the corresponding version of <quic_versions> array elements.
A client announces its available versions as follows: v1, v2, draft29.