r8169: add hw start helpers for the 8168 and the 8101

This commit triggers three 'defined but not used' warnings but
I prefer avoiding to tie these helpers to a specific change in
the hw start sequences of the 8168 or of the 8101.

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