Correct handling of QUIC transport parameters extension.

Correct handling of QUIC transport parameters extension.

Remove duplicate U16 length prefix, since tlsext_build() already adds this
for us. Condition on SSL_is_quic() rather than TLS version - RFC 9001 is
clear that this extension is only permitted on QUIC transport and an
fatal unsupported extension alert is required if used elsewhere.
Additionally, at the point where extensions are parsed, we do not
necessarily know what TLS version has been negotiated.

ok beck@ tb@