iavf: initialize waitqueues before starting watchdog_task

It is not safe to initialize the waitqueues after queueing the
watchdog_task. It will be using them.

The chance of this causing a real problem is very small, because
there will be some sleeping before any of the waitqueues get used.
I got a crash only after inserting an artificial sleep in iavf_probe.

Queue the watchdog_task as the last step in iavf_probe. Add a comment to
prevent repeating the mistake.

Fixes: fe2647ab

 ("i40evf: prevent VF close returning before state transitions to DOWN")
Signed-off-by: Michal Schmidt <mschmidt@redhat.com>
Reviewed-by: Paul Menzel <pmenzel@molgen.mpg.de>
Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>