r8169: reset bus if NIC isn't accessible after tx timeout

ASPM issues may result in the NIC not being accessible any longer.
In this case disabling ASPM may not work. Therefore detect this case
by checking whether register reads return ~0, and try to make the
NIC accessible again by resetting the secondary bus.

v2:
- add exception handling for the case that pci_reset_bus() fails

Suggested-by: Alexander Duyck <alexander.duyck@gmail.com>
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Reviewed-by: Alexander Duyck <alexanderduyck@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>