[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/af_x25.c b/net/x25/af_x25.c
index adcda8e..0d6002fc 100644
--- a/net/x25/af_x25.c
+++ b/net/x25/af_x25.c
@@ -951,7 +951,7 @@
 	 *	Incoming Call User Data.
 	 */
 	if (skb->len >= 0) {
-		memcpy(makex25->calluserdata.cuddata, skb->data, skb->len);
+		skb_copy_from_linear_data(skb, makex25->calluserdata.cuddata, skb->len);
 		makex25->calluserdata.cudlength = skb->len;
 	}