ixgbe: check return value of napi_complete_done()

The NIC driver should only enable interrupts when napi_complete_done()
returns true. This patch adds the check for ixgbe.

Cc: stable@vger.kernel.org # 4.10+
Suggested-by: NEric Dumazet <edumazet@google.com>
Signed-off-by: NSong Liu <songliubraving@fb.com>
Tested-by: NAndrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: NJeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/intel/ixgbe/ixgbe_main.c

@@ -3196,11 +3196,13 @@ int ixgbe_poll(struct napi_struct *napi, int budget)
 		return budget;
 
 	/* all work done, exit the polling mode */
-	napi_complete_done(napi, work_done);
-	if (adapter->rx_itr_setting & 1)
-		ixgbe_set_itr(q_vector);
-	if (!test_bit(__IXGBE_DOWN, &adapter->state))
-		ixgbe_irq_enable_queues(adapter, BIT_ULL(q_vector->v_idx));
+	if (likely(napi_complete_done(napi, work_done))) {
+		if (adapter->rx_itr_setting & 1)
+			ixgbe_set_itr(q_vector);
+		if (!test_bit(__IXGBE_DOWN, &adapter->state))
+			ixgbe_irq_enable_queues(adapter,
+						BIT_ULL(q_vector->v_idx));
+	}
 
 	return min(work_done, budget - 1);
 }