mac80211: Don't encrypt beacons

mac80211 should set the IEEE80211_TX_CTL_DO_NOT_ENCRYPT flag in tx_control
structure to inform drivers not to encrypt the beacon. Drivers that only check
for that flag before accessing the hw_key field, will otherwise cause a NULL
pointer dereference since that field is not configured for beacons.
Signed-off-by: NIvo van Doorn <IvDoorn@gmail.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

net/mac80211/tx.c

@@ -1898,6 +1898,7 @@ struct sk_buff *ieee80211_beacon_get(struct ieee80211_hw *hw,
 			control->flags |= IEEE80211_TXCTL_SHORT_PREAMBLE;
 		control->antenna_sel_tx = local->hw.conf.antenna_sel_tx;
 		control->flags |= IEEE80211_TXCTL_NO_ACK;
+		control->flags |= IEEE80211_TXCTL_DO_NOT_ENCRYPT;
 		control->retry_limit = 1;
 		control->flags |= IEEE80211_TXCTL_CLEAR_PS_FILT;
 	}