i40evf: ignore bogus messages from FW

Occasionally on shutdown, the FW will hand us a bunch of messages filled
with zeros, which can cause us to spin trying to handle them. Just
ignore these and get on with shutting down.

Change-ID: I347e9648f7153ad5a7b7e0847b87f7aad5f3e0da
Signed-off-by: Mitch Williams <mitch.a.williams@intel.com>
Tested-by: Jim Young <james.m.young@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/i40evf/i40evf_main.c

@@ -1631,7 +1631,7 @@ static void i40evf_adminq_task(struct work_struct *work)
 	v_msg = (struct i40e_virtchnl_msg *)&event.desc;
 	do {
 		ret = i40evf_clean_arq_element(hw, &event, &pending);
-		if (ret)
+		if (ret || !v_msg->v_opcode)
 			break; /* No event to process or error cleaning ARQ */
 
 		i40evf_virtchnl_completion(adapter, v_msg->v_opcode,