Ethtool: Implements ETHTOOL_PHY_GTUNABLE/ETHTOOL_PHY_STUNABLE and PHY downshift

Add ethtool get and set tunable to access PHY drivers.

Ethtool Help: ethtool -h for PHY tunables
    ethtool --set-phy-tunable DEVNAME      Set PHY tunable
                [ downshift on|off [count N] ]
    ethtool --get-phy-tunable DEVNAME      Get PHY tunable
                [ downshift ]

Ethtool ex:
  ethtool --set-phy-tunable eth0 downshift on
  ethtool --set-phy-tunable eth0 downshift off
  ethtool --set-phy-tunable eth0 downshift on count 2

  ethtool --get-phy-tunable eth0 downshift

Signed-off-by: Raju Lakkaraju <Raju.Lakkaraju@microsemi.com>
Signed-off-by: Allan W. Nielsen <allan.nielsen@microsemi.com>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Tested-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
2 files changed