mac80211: make align adjustment code support paged SKB

This fixed a BUG_ON in __skb_trim() when paged rx is used in
iwlwifi driver. Yes, the whole mac80211 stack doesn't support
paged SKB yet. But let's start the work slowly from small
code snippets.

Reported-and-tested-by: Abhijeet Kolekar <abhijeet.kolekar@intel.com>
Signed-off-by: Zhu Yi <yi.zhu@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/mac80211/rx.c

@@ -1326,10 +1326,10 @@ ieee80211_deliver_skb(struct ieee80211_rx_data *rx)
 				skb = NULL;
 			} else {
 				u8 *data = skb->data;
-				size_t len = skb->len;
-				u8 *new = __skb_push(skb, align);
-				memmove(new, data, len);
-				__skb_trim(skb, len);
+				size_t len = skb_headlen(skb);
+				skb->data -= align;
+				memmove(skb->data, data, len);
+				skb_set_tail_pointer(skb, len);
 			}
 		}
 #endif