net: systemport: fix dma_unmap_single() len

dma_unmap_single() was called with dma_unmap_len(cb, dma_len),
unfortunately we failed to assign this length field in
bcm_sysport_rx_refill() or bcm_sysport_alloc_rx_bufs() using
dma_unmap_len_set().

This causes packet contents corruption because are we not invoking the
cache invalidation routines with the proper length.  Fix this by using
the full RX buffer size (RX_BUF_LENGTH) because the mappings for the RX
bufers are created with that size.
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/broadcom/bcmsysport.c

@@ -479,7 +479,7 @@ static unsigned int bcm_sysport_desc_rx(struct bcm_sysport_priv *priv,
 		cb = &priv->rx_cbs[priv->rx_read_ptr];
 		skb = cb->skb;
 		dma_unmap_single(kdev, dma_unmap_addr(cb, dma_addr),
-				dma_unmap_len(cb, dma_len), DMA_FROM_DEVICE);
+				RX_BUF_LENGTH, DMA_FROM_DEVICE);
 
 		/* Extract the Receive Status Block prepended */
 		rsb = (struct rsb *)skb->data;