IEEE 802.11w/D6.0 defines new AKMPs to indicate SHA256-based algorithms for
key derivation (and AES-CMAC for EAPOL-Key MIC). Add support for using new
AKMPs and clean up AKMP processing with helper functions in defs.h.
This updates management frame protection to use the assocition ping process
from the latest draft (D6.0) to protect against unauthenticated
authenticate or (re)associate frames dropping association.
