When the interface is down, the hardware is powered off.
However, the suspend handler currently tries to send host sleep commands
(when wakeup params are set) in this configuration, causing a system hang
when going into suspend (the commands will never complete).

Avoid this by detecting this situation and simply returning from
the suspend handler without doing anything special.
Signed-off-by: Daniel Drake <dsd@laptop.org>
Acked-by: Dan Williams <dcbw@redhat.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>