r8169:call "rtl8168_driver_start" "rtl8168_driver_stop" only when hardware dash function is enabled

These two functions are used to inform dash firmware that driver is been
brought up or brought down. So call these two functions only when hardware dash
function is enabled.

Signed-off-by: Chun-Hao Lin <hau@realtek.com>
Signed-off-by: David S. Miller <davem@davemloft.net>