On "eap_tnc_process" function error case, data->in_buf keeps reference
to a local scope variable. For example this will cause segmentation
fault in "eap_tnc_deinit" function "wpabuf_free(data->in_buf)"
statement.
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).
