[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_in.c b/net/x25/x25_in.c
index b2bbe55..ba13248 100644
--- a/net/x25/x25_in.c
+++ b/net/x25/x25_in.c
@@ -112,8 +112,9 @@
 			 *	Copy any Call User Data.
 			 */
 			if (skb->len >= 0) {
-				memcpy(x25->calluserdata.cuddata, skb->data,
-				       skb->len);
+				skb_copy_from_linear_data(skb,
+					      x25->calluserdata.cuddata,
+					      skb->len);
 				x25->calluserdata.cudlength = skb->len;
 			}
 			if (!sock_flag(sk, SOCK_DEAD))