r8169: sync existing 8168 device hardware start sequences with vendor driver

This part of the driver should be reasonably in line with Realtek's
8.006.00 driver.

I have left some bits related to jumbo frame and optional features
aside for now.

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