[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/x25/x25_out.c b/net/x25/x25_out.c
index bb45e21..2b96b52 100644
--- a/net/x25/x25_out.c
+++ b/net/x25/x25_out.c
@@ -89,7 +89,7 @@
 
 			/* Duplicate the Header */
 			skb_push(skbn, header_len);
-			memcpy(skbn->data, header, header_len);
+			skb_copy_to_linear_data(skbn, header, header_len);
 
 			if (skb->len > 0) {
 				if (x25->neighbour->extended)