The previous version was deriving unnecessarily large amount of output data
for the implicit challenge. With the TLS PRF, this was not causing any
problems because the output length is not explicitly bound into the
derivation. Anyway, it is better to use the correct output length should
the PRF be ever changed to a one that uses the output length to change the
beginning of the output data.
Need to process EAP AVP after the non-EAP Phase 2 method. In addition,
EAP-TTLS/MSCHAPv2 needs special code for handling the starting of TNC after
extra roundtrip of MSCHAPv2 success message.
