r8169: modify the flow of the hw reset.

- Disable tx and rx by resetting hw, so replace rtl8169_asic_down
  with rtl8169_hw_reset.
- RxConfig bits 0 ~ 5 have to be cleared before hw reset to avoid
  receiving spurious data.
- Certain chips need to do some checking before reset.
- Remove hw reset which is done before hw_start. It is done in close,
  down or device probe functions.
- Move rtl8169_init_ring_indexes function into rtl_hw_reset function.
  The indexes of tx and rx only need to be zero when the hw resets.

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