net: systemport: avoid unbalanced enable_irq_wake calls

Multiple enable_irq_wake() calls will keep increasing the IRQ
wake_depth, which ultimately leads to the following types of
situation:

1) enable Wake-on-LAN interrupt w/o password
2) enable Wake-on-LAN interrupt w/ password
3) enable Wake-on-LAN interrupt w/o password
4) disable Wake-on-LAN interrupt

After step 4), SYSTEMPORT would always wake-up the system no matter what
wake-up device we use, which is not what we want. Fix this by making
sure there are no unbalanced enable_irq_wake() calls.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>