mac80211: fix radiotap vendor presence bitmap handling

Due to the alignment handling, it actually matters where in the code
we add the 4 bytes for the presence bitmap to the length; the first
field is the timestamp with 8 byte alignment so we need to add the
space for the extra vendor namespace presence bitmap *before* we do
any alignment for the fields.

Move the presence bitmap length accounting to the right place to fix
the alignment for the data properly.
Signed-off-by: NJohannes Berg <johannes.berg@intel.com>
Signed-off-by: NLuca Coelho <luciano.coelho@intel.com>
Signed-off-by: NJohannes Berg <johannes.berg@intel.com>

net/mac80211/rx.c

@@ -143,6 +143,9 @@ ieee80211_rx_radiotap_hdrlen(struct ieee80211_local *local,
 	/* allocate extra bitmaps */
 	if (status->chains)
 		len += 4 * hweight8(status->chains);
+	/* vendor presence bitmap */
+	if (status->flag & RX_FLAG_RADIOTAP_VENDOR_DATA)
+		len += 4;
 
 	if (ieee80211_have_rx_timestamp(status)) {
 		len = ALIGN(len, 8);
@@ -207,8 +210,6 @@ ieee80211_rx_radiotap_hdrlen(struct ieee80211_local *local,
 	if (status->flag & RX_FLAG_RADIOTAP_VENDOR_DATA) {
 		struct ieee80211_vendor_radiotap *rtap = (void *)skb->data;
 
-		/* vendor presence bitmap */
-		len += 4;
 		/* alignment for fixed 6-byte vendor data header */
 		len = ALIGN(len, 2);
 		/* vendor data header */