cfg80211: initialize rekey_data

In case we have old supplicant, the akm field is uninitialized.

Signed-off-by: Sara Sharon <sara.sharon@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20201129172929.930f0ab7ebee.Ic546e384efab3f4a89f318eafddc3eb7d556aecb@changeid


Signed-off-by: Johannes Berg <johannes.berg@intel.com>