net: ena: fix surprise unplug NULL dereference kernel crash

BugLink: http://bugs.launchpad.net/bugs/1792044

Starting with driver version 1.5.0, in case of a surprise device
unplug, there is a race caused by invoking ena_destroy_device()
from two different places. As a result, the readless register might
be accessed after it was destroyed.
Signed-off-by: Netanel Belgazal <netanel@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit 772ed869 linux-next)
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Acked-by: Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Brad Figg <brad.figg@canonical.com>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>

drivers/net/ethernet/amazon/ena/ena_netdev.c

@@ -3421,12 +3421,12 @@ static void ena_remove(struct pci_dev *pdev)
 		netdev->rx_cpu_rmap = NULL;
 	}
 #endif /* CONFIG_RFS_ACCEL */
-
-	unregister_netdev(netdev);
 	del_timer_sync(&adapter->timer_service);
 
 	cancel_work_sync(&adapter->reset_task);
 
+	unregister_netdev(netdev);
+
 	/* Reset the device only if the device is running. */
 	if (test_bit(ENA_FLAG_DEVICE_RUNNING, &adapter->flags))
 		ena_com_dev_reset(ena_dev, adapter->reset_reason);