mac80211: Don't request encryption for probe response

Probe responses shouldn't be encrypted, and mac80211 doesn't
set the crypto key accordingly. However it didn't set the
IEEE80211_TX_CTL_DO_NOT_ENCRYPT flag which means drivers
could make an attempt to encrypt it, and causing a NULL
pointer dereference when accessing the provided hw_key field.

Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Acked-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/mac80211/mlme.c

@@ -2481,6 +2481,7 @@ static int ieee80211_sta_join_ibss(struct net_device *dev,
 			control->flags |= IEEE80211_TX_CTL_SHORT_PREAMBLE;
 		control->antenna_sel_tx = local->hw.conf.antenna_sel_tx;
 		control->flags |= IEEE80211_TX_CTL_NO_ACK;
+		control->flags |= IEEE80211_TX_CTL_DO_NOT_ENCRYPT;
 		control->control.retry_limit = 1;
 
 		ifsta->probe_resp = skb_copy(skb, GFP_ATOMIC);