[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/usb/net/catc.c b/drivers/usb/net/catc.c
index d82022d..ffec2e0 100644
--- a/drivers/usb/net/catc.c
+++ b/drivers/usb/net/catc.c
@@ -418,7 +418,7 @@
 	catc->tx_ptr = (((catc->tx_ptr - 1) >> 6) + 1) << 6;
 	tx_buf = catc->tx_buf[catc->tx_idx] + catc->tx_ptr;
 	*((u16*)tx_buf) = (catc->is_f5u011) ? cpu_to_be16((u16)skb->len) : cpu_to_le16((u16)skb->len);
-	memcpy(tx_buf + 2, skb->data, skb->len);
+	skb_copy_from_linear_data(skb, tx_buf + 2, skb->len);
 	catc->tx_ptr += skb->len + 2;
 
 	if (!test_and_set_bit(TX_RUNNING, &catc->flags))