ixgbe: fix possible deadlock in ixgbe_service_task()

ixgbe_service_task() calls unregister_netdev() under rtnl_lock().
But unregister_netdev() internally calls rtnl_lock().
So deadlock would occur.

Fixes: 59dd45d550 ("ixgbe: firmware recovery mode")
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

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

@@ -7897,11 +7897,8 @@ static void ixgbe_service_task(struct work_struct *work)
 		return;
 	}
 	if (ixgbe_check_fw_error(adapter)) {
-		if (!test_bit(__IXGBE_DOWN, &adapter->state)) {
-			rtnl_lock();
+		if (!test_bit(__IXGBE_DOWN, &adapter->state))
 			unregister_netdev(adapter->netdev);
-			rtnl_unlock();
-		}
 		ixgbe_service_event_complete(adapter);
 		return;
 	}