net: hns3: add ethtool_ops.get_coalesce support to PF

This patch adds ethtool_ops.get_coalesce support to PF.

Whilst our hardware supports per queue values, external interfaces
support only a single shared value. As such we use the values for
queue 0.

Signed-off-by: Fuyun Liang <liangfuyun1@huawei.com>
Signed-off-by: Peng Li <lipeng321@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>