[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/netrom/nr_loopback.c b/net/netrom/nr_loopback.c
index 99fdab1..f324d5d 100644
--- a/net/netrom/nr_loopback.c
+++ b/net/netrom/nr_loopback.c
@@ -34,7 +34,7 @@
 	struct sk_buff *skbn;
 
 	if ((skbn = alloc_skb(skb->len, GFP_ATOMIC)) != NULL) {
-		memcpy(skb_put(skbn, skb->len), skb->data, skb->len);
+		skb_copy_from_linear_data(skb, skb_put(skbn, skb->len), skb->len);
 		skb_reset_transport_header(skbn);
 
 		skb_queue_tail(&loopback_queue, skbn);