r8169: improve handling of CPCMD quirk mask

Both quirk masks are the same, so we can merge them. The quirk mask
includes most bits so it's actually easier to define a mask with
the bits to keep.

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