net: hns3: Remove a useless member of struct hns3_stats

The member "stats_size" of struct hns3_stats is useless,
remove it and fix the macro definition which has uses this
struct.

Signed-off-by: Jian Shen <shenjian15@huawei.com>
Signed-off-by: Peng Li <lipeng321@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>