sh-eth: use netdev stats structure and fix dma_map_single

No need to maintain a parallel net_device_stats structure in
sh_eth_private, since we have a generic one in netdev

Fix two dma_map_single() incorrect parameters, passing skb->tail instead
of skb->data. Seems that there is no corresponding dmap_unmap_single()
calls for the moment in this driver.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Tested-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: David S. Miller <davem@davemloft.net>