Fix TNC with EAP-TTLS

Fix TNC with EAP-TTLS

This was broken by 510c02d4a362cd572303fa845b139eacb2dab387 which added
validation of eap_ttls_phase2_eap_init() return value. The main problem
in the code trying to initialize a new phase 2 EAP method
unconditionally; this should only happen if there is a new method in the
inner method sequence.