Add a utility to append a KDE to the key_data field in an EAPoL frame.
The KDE types enum is actually added to handshake.h because we've got
the utilities for finding those KDEs in a buffer there. The new
function is specific to EAPoL-Key frames though and perhaps to simple to
be split across handshake.c and eapol.c. Also it didn't seem useful to
use the ie_tlv_builder here.
Split the igtk parameter to handshake_state_install_igtk into one
parameter for the actual IGTK buffer and one for the IPN buffer instead
of requiring the caller to have them both in one continuous buffer.
With FT protocol, one is received encrypted and the other in plain text.
struct handshake_state is an object that stores all the key data and other
authentication state and does the low level operations on the keys. Together
with the next patch this mostly just splits eapol.c into two layers
so that the key operations can also be used in Fast Transitions which don't
use eapol.
