cfg80211: Rename SAE_DATA to more generic AUTH_DATA

This adds defines and nl80211 extensions to allow FILS Authentication to
be implemented similarly to SAE. FILS does not need the special rules
for the Authentication transaction number and Status code fields, but it
does need to add non-IE fields. The previously used
NL80211_ATTR_SAE_DATA can be reused for this to avoid having to
duplicate that implementation. Rename that attribute to more generic
NL80211_ATTR_AUTH_DATA (with backwards compatibility define for
NL80211_SAE_DATA).

Also document the special rules related to the Authentication
transaction number and Status code fiels.

Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>