net: hns3: add support to query and set lane number by ethtool

When serdes lane support setting 25Gb/s or 50Gb/s speed and user wants to
set port speed as 50Gb/s, it can be setted as one 50Gb/s serdes lane or
two 25Gb/s serdes lanes.

So, this patch adds support to query and set lane number by ethtool
to satisfy this scenario.

Signed-off-by: Hao Chen <chenhao418@huawei.com>
Signed-off-by: Guangbin Huang <huangguangbin2@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>