When initializing the MAC, the MTU vlaue need to be set to the hardware
too. Otherwise, the MTU value of software will be different from the MTU
value of hardware.

Fixes: 46a3df9f ("net: hns3: Add HNS3 Acceleration Engine & Compatibility Layer Support")
Signed-off-by: NFuyun Liang <liangfuyun1@huawei.com>
Signed-off-by: NPeng Li <lipeng321@huawei.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>