[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/hamradio/dmascc.c b/drivers/net/hamradio/dmascc.c
index 0fbb414..3be8c50 100644
--- a/drivers/net/hamradio/dmascc.c
+++ b/drivers/net/hamradio/dmascc.c
@@ -930,7 +930,7 @@
 
 	/* Transfer data to DMA buffer */
 	i = priv->tx_head;
-	memcpy(priv->tx_buf[i], skb->data + 1, skb->len - 1);
+	skb_copy_from_linear_data_offset(skb, 1, priv->tx_buf[i], skb->len - 1);
 	priv->tx_len[i] = skb->len - 1;
 
 	/* Clear interrupts while we touch our circular buffers */