r8169: move disabling interrupt coalescing to RTL8169/RTL8168 init

RTL8125 doesn't support the same coalescing registers, therefore move
this initialization to the 8168/6169-specific init.

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