mac80211: Allow station mode SAE to be implemented in user space

SAE uses two rounds of Authentication frames and both rounds require
considerable calculation to be done. This commit extends the existing
station mode authentication request to allow more control for user
space programs to build the SAE fields and to run the authentication
step ones. Only the second round with authentication transaction
sequence 2 will result in moving to authenticated state.

Signed-off-by: Jouni Malinen <j@w1.fi>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>