[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/ipv6/ipcomp6.c b/net/ipv6/ipcomp6.c
index 7691a1b..1ee50b5 100644
--- a/net/ipv6/ipcomp6.c
+++ b/net/ipv6/ipcomp6.c
@@ -111,7 +111,7 @@
 
 	skb->truesize += dlen - plen;
 	__skb_put(skb, dlen - plen);
-	memcpy(skb->data, scratch, dlen);
+	skb_copy_to_linear_data(skb, scratch, dlen);
 	err = ipch->nexthdr;
 
 out_put_cpu: