[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/ipv4/netfilter/ip_queue.c b/net/ipv4/netfilter/ip_queue.c
index cd8fec0..0d72693 100644
--- a/net/ipv4/netfilter/ip_queue.c
+++ b/net/ipv4/netfilter/ip_queue.c
@@ -368,7 +368,7 @@
 	}
 	if (!skb_make_writable(&e->skb, v->data_len))
 		return -ENOMEM;
-	memcpy(e->skb->data, v->payload, v->data_len);
+	skb_copy_to_linear_data(e->skb, v->payload, v->data_len);
 	e->skb->ip_summed = CHECKSUM_NONE;
 
 	return 0;