r8169: improve setting interrupt mask

So far several places in the code deal with setting the interrupt mask
for the respective chip versions. Improve this by having one function
for this only. In addition don't set RxFIFOOver for all 8101 chip
versions like in the vendor driver.

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