net: hns3: add support for FEC encoding control

This patch adds support for FEC encoding control, user can change
FEC mode by command ethtool --set-fec, and get FEC mode by command
ethtool --show-fec. The fec capability is changed follow the port
speed. If autoneg on, the user configure fec mode will be overwritten
by autoneg result.

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