tg3: Disable tg3 device on system reboot to avoid triggering AER

Commit d60cd063

 ("PM: ACPI: reboot: Use S5 for reboot") caused a
reboot hang on one Dell servers so the commit was reverted.

Someone managed to collect the AER log and it's caused by MSI:
[ 148.762067] ACPI: Preparing to enter system sleep state S5
[ 148.794638] {1}[Hardware Error]: Hardware error from APEI Generic Hardware Error Source: 5
[ 148.803731] {1}[Hardware Error]: event severity: recoverable
[ 148.810191] {1}[Hardware Error]: Error 0, type: fatal
[ 148.816088] {1}[Hardware Error]: section_type: PCIe error
[ 148.822391] {1}[Hardware Error]: port_type: 0, PCIe end point
[ 148.829026] {1}[Hardware Error]: version: 3.0
[ 148.834266] {1}[Hardware Error]: command: 0x0006, status: 0x0010
[ 148.841140] {1}[Hardware Error]: device_id: 0000:04:00.0
[ 148.847309] {1}[Hardware Error]: slot: 0
[ 148.852077] {1}[Hardware Error]: secondary_bus: 0x00
[ 148.857876] {1}[Hardware Error]: vendor_id: 0x14e4, device_id: 0x165f
[ 148.865145] {1}[Hardware Error]: class_code: 020000
[ 148.870845] {1}[Hardware Error]: aer_uncor_status: 0x00100000, aer_uncor_mask: 0x00010000
[ 148.879842] {1}[Hardware Error]: aer_uncor_severity: 0x000ef030
[ 148.886575] {1}[Hardware Error]: TLP Header: 40000001 0000030f 90028090 00000000
[ 148.894823] tg3 0000:04:00.0: AER: aer_status: 0x00100000, aer_mask: 0x00010000
[ 148.902795] tg3 0000:04:00.0: AER: [20] UnsupReq (First)
[ 148.910234] tg3 0000:04:00.0: AER: aer_layer=Transaction Layer, aer_agent=Requester ID
[ 148.918806] tg3 0000:04:00.0: AER: aer_uncor_severity: 0x000ef030
[ 148.925558] tg3 0000:04:00.0: AER: TLP Header: 40000001 0000030f 90028090 00000000

The MSI is probably raised by incoming packets, so power down the device
and disable bus mastering to stop the traffic, as user confirmed this
approach works.

In addition to that, be extra safe and cancel reset task if it's running.

Cc: Josef Bacik <josef@toxicpanda.com>
Link: https://lore.kernel.org/all/b8db79e6857c41dab4ef08bdf826ea7c47e3bafc.1615947283.git.josef@toxicpanda.com/
BugLink: https://bugs.launchpad.net/bugs/1917471
Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Reviewed-by: Michael Chan <michael.chan@broadcom.com>
Link: https://lore.kernel.org/r/20220826002530.1153296-1-kai.heng.feng@canonical.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>