net: hns: bug fix about TSO on|off when there is traffic

When enable/disable tso, the driver tries to access the hardware register,
but this operation will cause the port unavalible when there is traffic.
This patch tries to enable TSO when initialize, then control tso through
TSE bit in transmit descriptor.

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>