r8169: change default behavior for mildly identified 8168c chipsets

The addition of a new device has so far implied a specialization of
these masks. While they identify 8168c devices, they can be expected
to be further refined as they have been by Realtek so far.

The change should bring the driver closer to the version 8.006.00 of
Realtek's 8168 driver.

Signed-off-by: Francois Romieu <romieu@fr.zoreil.com>
Cc: Edward Hsu <edward_hsu@realtek.com.tw>