r8169: enable WAKE_PHY as only WoL source when runtime-suspending

We go to runtime-suspend few secs after cable removal. As cable is
removed "physical link up" is the only meaningful WoL source.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>