[SK_BUFF]: Introduce skb_copy_to_linear_data{_offset}

To clearly state the intent of copying to linear sk_buffs, _offset being a
overly long variant but interesting for the sake of saving some bytes.

Signed-off-by: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
diff --git a/net/ieee80211/ieee80211_rx.c b/net/ieee80211/ieee80211_rx.c
index 94e2b8e..6ae036b 100644
--- a/net/ieee80211/ieee80211_rx.c
+++ b/net/ieee80211/ieee80211_rx.c
@@ -759,8 +759,9 @@
 		    IEEE80211_FCTL_TODS) && skb->len >= ETH_HLEN + ETH_ALEN) {
 		/* Non-standard frame: get addr4 from its bogus location after
 		 * the payload */
-		memcpy(skb->data + ETH_ALEN,
-		       skb->data + skb->len - ETH_ALEN, ETH_ALEN);
+		skb_copy_to_linear_data_offset(skb, ETH_ALEN,
+					       skb->data + skb->len - ETH_ALEN,
+					       ETH_ALEN);
 		skb_trim(skb, skb->len - ETH_ALEN);
 	}
 #endif