net: hisilicon: Offset buf address to adapt HI13X1_GMAC

The buf unit size of HI13X1_GMAC is cache_line_size,
which is 64, so the address we write to the buf register
needs to be shifted right by 6 bits.

The 31st bit of the PPE_CFG_CPU_ADD_ADDR register
of HI13X1_GMAC indicates whether to release the buffer
of the message, and the low indicates that it is valid.

Signed-off-by: Jiangfeng Xiao <xiaojiangfeng@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>