iavf: centralize watchdog requeueing itself

Centralize the unlock(critlock); unlock(netdev); queue_delayed_work(watchog_task);
pattern to one place.

Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Signed-off-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Tested-by: Rafal Romanowski <rafal.romanowski@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>