net/ncsi: add NCSI Intel OEM command to keep PHY up

This allows to keep PHY link up and prevents any channel resets during
the host load.

It is KEEP_PHY_LINK_UP option(Veto bit) in i210 datasheet which
block PHY reset and power state changes.

Signed-off-by: Ivan Mikhaylov <i.mikhaylov@yadro.com>
Signed-off-by: David S. Miller <davem@davemloft.net>