Add the "concat" flag

For EAP-Message, and RFC 5904 attributes.  It means that the
encoder/decoder takes care of splitting / concatenating
the attributes
Use correct variable when decoding inner tunnel things
"concatenated" attributes get split when encoded

But only if they're more than 253 octets long.
The dictionary parser enforces the limitation that only
"RFC" attributes can be concatenated
Make eap_compose routine for EAP is now RADIUS un-aware

It relies on the packet encoder to chop the EAP packet into
attributes
Notes on 253 octets and TTLS