Fixed EAP-TNC not to include extra EAP header and TNC flags

Fixed EAP-TNC not to include extra EAP header and TNC flags

The change to support fragmentation added extra function to generate the
EAP header, but forgot to remove the original code and ended up getting two
EAP headers and TNC flags field in the generated message. These header
fields need to be added only in the function that builds the final message
(and if necessary, fragments the data).