NET/r8169: Rework suspend and resume

NET/r8169: Rework suspend and resume

The recent changes of the PCI PM core allow us to simplify the
suspend and resume handling in a number of device drivers, since they
don't need to carry out the general PCI PM operations, such as
changing the power state of the device, during suspend and resume any
more.

Simplify the suspend and resume callbacks of r8169 using the
observation that the PCI PM core can take care of some operations
carried out by the driver.

Additionally, make the shutdown callback of r8169 only put the device
into a low power state if the system is going to be powered off
(kexec is known to have problems with network adapters that are put
into low power states on shutdown).

This patch has been tested on MSI Wind U100.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Tested-by: Bruno Prémont <bonbons@linux-vserver.org>
Signed-off-by: David S. Miller <davem@davemloft.net>