[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/bridge/br_netfilter.c b/net/bridge/br_netfilter.c
index 8cee7fd..8b45224 100644
--- a/net/bridge/br_netfilter.c
+++ b/net/bridge/br_netfilter.c
@@ -129,7 +129,8 @@
 	if (skb->protocol == htons(ETH_P_8021Q))
 		header_size += VLAN_HLEN;
 
-	memcpy(skb->nf_bridge->data, skb->data - header_size, header_size);
+	skb_copy_from_linear_data_offset(skb, -header_size,
+					 skb->nf_bridge->data, header_size);
 }
 
 /*