Added a new configuration option, wpa_ptk_rekey, that can be used to
enforce frequent PTK rekeying, e.g., to mitigate some attacks against TKIP
deficiencies. This can be set either by the Authenticator (to initiate
periodic 4-way handshake to rekey PTK) or by the Supplicant (to request
Authenticator to rekey PTK).
With both wpa_ptk_rekey and wpa_group_rekey (in hostapd) set to 600, TKIP
keys will not be used for more than 10 minutes which may make some attacks
against TKIP more difficult to implement.
Setting the value of the SET_NETWORK command to NULL (without quotation)
unsets the variable, i.e., removes it from configuration file. This is
needed to allow GUI programs to clear variables, e.g., identity for
EAP-AKA/SIM.
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.
