[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/ipmr.c b/net/ipv4/ipmr.c
index 48027df..0ebae41 100644
--- a/net/ipv4/ipmr.c
+++ b/net/ipv4/ipmr.c
@@ -584,7 +584,7 @@
 
 	skb->network_header = skb->tail;
 	skb_put(skb, ihl);
-	memcpy(skb->data,pkt->data,ihl);
+	skb_copy_to_linear_data(skb, pkt->data, ihl);
 	ip_hdr(skb)->protocol = 0;			/* Flag to the kernel this is a route add */
 	msg = (struct igmpmsg *)skb_network_header(skb);
 	msg->im_vif = vifi;