net: hns3: fix flow control configure issue for fibre port

Flow control autoneg is unsupported for fibre port. It takes no
effect for flow control when restart autoneg. This patch fixes
it, return -EOPNOTSUPP when user tries to enable flow control
autoneg.

Signed-off-by: Jian Shen <shenjian15@huawei.com>
Signed-off-by: Peng Li <lipeng321@huawei.com>
Signed-off-by: Huazhong Tan <tanhuazhong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>