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 allows hostapd to share the PMKSA caches internally when multiple BSSes or radios are being controlled by the same hostapd process.
