i40e: prevent service task from running while we're suspended

Although the service task does check the suspended status before
running, it might already be part way through running when we go to
suspend. Lets ensure that the service task is stopped and will not be
restarted again until we finish resuming. This ensures that service task
code does not cause strange interactions with the suspend/resume
handlers.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>