net: hns: change the default coalesce usecs

The default coalesce timeout is 3us, which is will cause CPU
usage is too high. This patch change it to 50us in order to reduce
CPU usage and the value makes sure network latency also meets requirement.

Signed-off-by: Daode Huang <huangdaode@hisilicon.com>
Signed-off-by: Yisen Zhuang <Yisen.Zhuang@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>