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

net/wireless/nl80211.c

@@ -12634,7 +12634,7 @@ static int nl80211_set_rekey_data(struct sk_buff *skb, struct genl_info *info)
 	struct net_device *dev = info->user_ptr[1];
 	struct wireless_dev *wdev = dev->ieee80211_ptr;
 	struct nlattr *tb[NUM_NL80211_REKEY_DATA];
-	struct cfg80211_gtk_rekey_data rekey_data;
+	struct cfg80211_gtk_rekey_data rekey_data = {};
 	int err;
 
 	if (!info->attrs[NL80211_ATTR_REKEY_DATA])