r8169: make use of phy_set_asym_pause

phy_probe() takes care that all supported modes are advertised,
in addition use phy_support_asym_pause() to advertise pause modes.
This way we don't have to deal with phylib internals directly.

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