mac80211: fix paged defragmentation

Paged RX skb patch broke the defragmentation. We need to read hdr again
after linearization.

It fixes following bug
http://bugzilla.intellinuxwireless.org/show_bug.cgi?id=2194

Signed-off-by: Zhu, Yi <yi.zhu@intel.com>
Signed-off-by: Abhijeet Kolekar <abhijeet.kolekar@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/mac80211/rx.c

@@ -1252,6 +1252,12 @@ ieee80211_rx_h_defragment(struct ieee80211_rx_data *rx)
 	if (skb_linearize(rx->skb))
 		return RX_DROP_UNUSABLE;
 
+	/*
+	 *  skb_linearize() might change the skb->data and
+	 *  previously cached variables (in this case, hdr) need to
+	 *  be refreshed with the new data.
+	 */
+	hdr = (struct ieee80211_hdr *)rx->skb->data;
 	seq = (sc & IEEE80211_SCTL_SEQ) >> 4;
 
 	if (frag == 0) {