r8169: do not enable the TBI for anything but the original 8169.

The TBI bit in PHYStatus is reserved on anything but the oldest 8169.

Nobody complained after I disabled it for the 8168 and the 810x (see
66ec5d4f

).

Signed-off-by: Francois Romieu <romieu@fr.zoreil.com>
Cc: Hayes Wang <hayeswang@realtek.com>