net: ena: use SHUTDOWN as reset reason when closing interface

The 'ENA_REGS_RESET_SHUTDOWN' enum indicates a normal driver
shutdown / removal procedure.

Also, a comment is added to one of the reset reason assignments for
code clarity.
Signed-off-by: NShay Agroskin <shayagr@amazon.com>
Signed-off-by: NArthur Kiyanovski <akiyano@amazon.com>
Signed-off-by: NSameeh Jubran <sameehj@amazon.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

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

@@ -3439,6 +3439,7 @@ static void ena_destroy_device(struct ena_adapter *adapter, bool graceful)
 
 	ena_com_mmio_reg_read_request_destroy(ena_dev);
 
+	/* return reset reason to default value */
 	adapter->reset_reason = ENA_REGS_RESET_NORMAL;
 
 	clear_bit(ENA_FLAG_TRIGGER_RESET, &adapter->flags);
@@ -4362,6 +4363,7 @@ static void __ena_shutoff(struct pci_dev *pdev, bool shutdown)
 	cancel_work_sync(&adapter->reset_task);
 
 	rtnl_lock(); /* lock released inside the below if-else block */
+	adapter->reset_reason = ENA_REGS_RESET_SHUTDOWN;
 	ena_destroy_device(adapter, true);
 	if (shutdown) {
 		netif_device_detach(netdev);