r8169: never set PCI_EXP_DEVCTL_NOSNOOP_EN

Setting PCI_EXP_DEVCTL_NOSNOOP_EN for certain chip versions had been
added to the vendor driver more than 10 years ago, and copied from
there to r8169. It has been removed from the vendor driver meanwhile
and I think we can safely remove this too.

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