mac80211: fix injection in monitor mode

The location of the 802.11 header is calculated incorrectly due to a
wrong placement of parentheses.  Found by kmemcheck.
Signed-off-by: Pavel Roskin <proski@gnu.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/mac80211/tx.c

@@ -1455,7 +1455,7 @@ int ieee80211_master_start_xmit(struct sk_buff *skb, struct net_device *dev)
 		monitor_iface = UNKNOWN_ADDRESS;
 
 		len_rthdr = ieee80211_get_radiotap_len(skb->data);
-		hdr = (struct ieee80211_hdr *)skb->data + len_rthdr;
+		hdr = (struct ieee80211_hdr *)(skb->data + len_rthdr);
 		hdrlen = ieee80211_hdrlen(hdr->frame_control);
 
 		/* check the header is complete in the frame */