According to Documentation/power/devices.txt

The driver should not use device_set_wakeup_enable() which is the policy
for user to decide.

Using device_init_wakeup() to initialize dev->power.should_wakeup and
dev->power.can_wakeup on driver initialization.

And use device_may_wakeup() on suspend to decide if WoL function should
be enabled on NIC.
Reported-by: Diego Viola <diego.viola@gmail.com>
Signed-off-by: Guo-Fu Tseng <cooldavid@cooldavid.org>
Signed-off-by: David S. Miller <davem@davemloft.net>