iavf: schedule watchdog immediately when changing primary MAC

iavf_replace_primary_mac() utilizes queue_work() to schedule the
watchdog task but that only ensures that the watchdog task is queued
to run. To make sure the watchdog is executed asap use
mod_delayed_work().

Without this patch it may take up to 2s until the watchdog task gets
executed, which may cause long delays when setting the MAC address.

Fixes: a3e839d5

 ("iavf: Add usage of new virtchnl format to set default MAC")
Signed-off-by: Stefan Assmann <sassmann@kpanic.de>
Reviewed-by: Michal Schmidt <mschmidt@redhat.com>
Tested-by: Michal Schmidt <mschmidt@redhat.com>
Tested-by: Rafal Romanowski <rafal.romanowski@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>