tg3: Disable tg3 PCIe AER on system reboot

tg3: Disable tg3 PCIe AER on system reboot

Disable PCIe AER on the tg3 device on system reboot on a limited
list of Dell PowerEdge systems. This prevents a fatal PCIe AER event
on the tg3 device during the ACPI _PTS (prepare to sleep) method for
S5 on those systems. The _PTS is invoked by acpi_enter_sleep_state_prep()
as part of the kernel's reboot sequence as a result of commit
38f34dba806a ("PM: ACPI: reboot: Reinstate S5 for reboot").

There was an earlier fix for this problem by commit 2ca1c94ce0b6
("tg3: Disable tg3 device on system reboot to avoid triggering AER").
But it was discovered that this earlier fix caused a reboot hang
when some Dell PowerEdge servers were booted via ipxe. To address
this reboot hang, the earlier fix was essentially reverted by commit
9fc3bc764334 ("tg3: power down device only on SYSTEM_POWER_OFF").
This re-exposed the tg3 PCIe AER on reboot problem.

This fix is not an ideal solution because the root cause of the AER
is in system firmware. Instead, it's a targeted work-around in the
tg3 driver.

Note also that the PCIe AER must be disabled on the tg3 device even
if the system is configured to use "firmware first" error handling.

V3:
   - Fix sparse warning on improper comparison of pdev->current_state
   - Adhere to netdev comment style

Fixes: 9fc3bc764334 ("tg3: power down device only on SYSTEM_POWER_OFF")
Signed-off-by: Lenny Szubowicz <lszubowi@redhat.com>
Reviewed-by: Pavan Chebbi <pavan.chebbi@broadcom.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>