EAP-TNC: Add Flags field into fragment acknowledgement

EAP-TNC: Add Flags field into fragment acknowledgement

TNC IF-T is somewhat unclear on this are, but
draft-hanna-nea-pt-eap-00.txt, which is supposed to define the same
protocol, is clearer on the Flags field being included.

This change breaks interoperability with the old implementation if
EAP-TNC fragmentation is used. The old version would not accept
the acknowledgement message with the added Flags octet while the
new version accepts messagss with with both options.