[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/drivers/net/wan/pc300_drv.c b/drivers/net/wan/pc300_drv.c
index edbc555..8ba75bb 100644
--- a/drivers/net/wan/pc300_drv.c
+++ b/drivers/net/wan/pc300_drv.c
@@ -1765,7 +1765,7 @@
 	skb->data[7] = ']';
 	skb->data[8] = ':';
 	skb->data[9] = ' ';
-	memcpy(&skb->data[10], skb_main->data, skb_main->len);
+	skb_copy_from_linear_data(skb_main, &skb->data[10], skb_main->len);
 
 	netif_rx(skb);
 }