net: hns3: Add support to change MTU in HNS3 hardware

This patch adds the following support to the HNS3 driver:
1. Support to change the Maximum Transmission Unit of a
   port in the HNS NIC hardware.
2. Initializes the supported MTU range for the netdevice.

Signed-off-by: lipeng <lipeng321@huawei.com>
Signed-off-by: Salil Mehta <salil.mehta@huawei.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>