[SK_BUFF]: Introduce skb_copy_from_linear_data{_offset}

To clearly state the intent of copying from 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@redhat.com>
diff --git a/net/ieee80211/ieee80211_tx.c b/net/ieee80211/ieee80211_tx.c
index 62a8a2b..a4c3c51 100644
--- a/net/ieee80211/ieee80211_tx.c
+++ b/net/ieee80211/ieee80211_tx.c
@@ -309,8 +309,8 @@
 	}
 
 	/* Save source and destination addresses */
-	memcpy(dest, skb->data, ETH_ALEN);
-	memcpy(src, skb->data + ETH_ALEN, ETH_ALEN);
+	skb_copy_from_linear_data(skb, dest, ETH_ALEN);
+	skb_copy_from_linear_data_offset(skb, ETH_ALEN, src, ETH_ALEN);
 
 	if (host_encrypt || host_build_iv)
 		fc = IEEE80211_FTYPE_DATA | IEEE80211_STYPE_DATA |
@@ -363,7 +363,7 @@
 		snapped = 1;
 		ieee80211_copy_snap(skb_put(skb_new, SNAP_SIZE + sizeof(u16)),
 				    ether_type);
-		memcpy(skb_put(skb_new, skb->len), skb->data, skb->len);
+		skb_copy_from_linear_data(skb, skb_put(skb_new, skb->len), skb->len);
 		res = crypt->ops->encrypt_msdu(skb_new, hdr_len, crypt->priv);
 		if (res < 0) {
 			IEEE80211_ERROR("msdu encryption failed\n");
@@ -492,7 +492,7 @@
 			bytes -= SNAP_SIZE + sizeof(u16);
 		}
 
-		memcpy(skb_put(skb_frag, bytes), skb->data, bytes);
+		skb_copy_from_linear_data(skb, skb_put(skb_frag, bytes), bytes);
 
 		/* Advance the SKB... */
 		skb_pull(skb, bytes);