iwlwifi: sleep for at least 10 seconds

Many platforms have issues processing a wakeup signal
while they're still suspending, and will ignore it.
Since our device thinks it woke the platform, and the
platform ignored the signal, it will sleep without
WoWLAN being enabled as the device disables WoWLAN
when having woken the platform.

Resolve this by making the device wait for 10 seconds
after getting the suspend signal before waking up the
platform.

Reviewed-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>