net: core: add member wol_enabled to struct net_device

Add flag wol_enabled to struct net_device indicating whether
Wake-on-LAN is enabled. As first user phy_suspend() will use it to
decide whether PHY can be suspended or not.

Fixes: f1e911d5 ("r8169: add basic phylib support")
Fixes: e8cfd9d6c772 ("net: phy: call state machine synchronously in phy_stop")
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>