[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/irda/donauboe.c b/drivers/net/irda/donauboe.c
index ddfa6c3..9987a0d 100644
--- a/drivers/net/irda/donauboe.c
+++ b/drivers/net/irda/donauboe.c
@@ -1119,7 +1119,7 @@
   else
     {
       len = skb->len;
-      memcpy (self->tx_bufs[self->txs], skb->data, len);
+      skb_copy_from_linear_data(skb, self->tx_bufs[self->txs], len);
     }
   self->ring->tx[self->txs].len = len & 0x0fff;