ENET_RX_BUF_DMA_OFFSET
slot->dma_addr = dma_map_single(dev, slot->buf + ENET_RX_BUF_DMA_OFFSET,
#define ENET_RX_BUF_DMA_SIZE (ENET_RX_SKB_BUF_SIZE - ENET_RX_BUF_DMA_OFFSET)
skb_reserve(skb, ENET_RX_BUF_DMA_OFFSET);