net: hns3: add support to update flow control settings after autoneg

When auto-negotiation is enabled, the MAC flow control settings is
based on the flow control negotiation result. And it should be configured
after a valid link has been established. This patch adds support to update
flow control settings after auto-negotiation has completed.

Signed-off-by: Peng Li <lipeng321@huawei.com>
Signed-off-by: Fuyun Liang <liangfuyun1@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>