[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/x25/x25_out.c b/net/x25/x25_out.c
index 6f57378..bb45e21 100644
--- a/net/x25/x25_out.c
+++ b/net/x25/x25_out.c
@@ -61,7 +61,7 @@
 
 	if (skb->len - header_len > max_len) {
 		/* Save a copy of the Header */
-		memcpy(header, skb->data, header_len);
+		skb_copy_from_linear_data(skb, header, header_len);
 		skb_pull(skb, header_len);
 
 		frontlen = skb_headroom(skb);
@@ -84,7 +84,7 @@
 			len = max_len > skb->len ? skb->len : max_len;
 
 			/* Copy the user data */
-			memcpy(skb_put(skbn, len), skb->data, len);
+			skb_copy_from_linear_data(skb, skb_put(skbn, len), len);
 			skb_pull(skb, len);
 
 			/* Duplicate the Header */