[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/sunlance.c b/drivers/net/sunlance.c
index 8f53a1e..4272253 100644
--- a/drivers/net/sunlance.c
+++ b/drivers/net/sunlance.c
@@ -1143,7 +1143,7 @@
 		struct lance_init_block *ib = lp->init_block_mem;
 		ib->btx_ring [entry].length = (-len) | 0xf000;
 		ib->btx_ring [entry].misc = 0;
-		memcpy((char *)&ib->tx_buf [entry][0], skb->data, skblen);
+		skb_copy_from_linear_data(skb, &ib->tx_buf [entry][0], skblen);
 		if (len != skblen)
 			memset((char *) &ib->tx_buf [entry][skblen], 0, len - skblen);
 		ib->btx_ring [entry].tmd1_bits = (LE_T1_POK | LE_T1_OWN);