net: hns3: refactor the coalesce related struct

This patch refoctors the coalesce related struct by introducing
the hns3_enet_coalesce struct, in order to fix the coalesce
configuation lost problem when changing the channel number.

Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
Signed-off-by: Peng Li <lipeng321@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>