It appears that not disabling a PCI device on .shutdown may lead to
a Hardware Error with particular (perhaps buggy) BIOS versions:

    mlx4_en: eth0: Close port called
    mlx4_en 0000:04:00.0: removed PHC
    reboot: Restarting system
    {1}[Hardware Error]: Hardware error from APEI Generic Hardware Error Source: 1
    {1}[Hardware Error]: event severity: fatal
    {1}[Hardware Error]:  Error 0, type: fatal
    {1}[Hardware Error]:   section_type: PCIe error
    {1}[Hardware Error]:   port_type: 4, root port
    {1}[Hardware Error]:   version: 1.16
    {1}[Hardware Error]:   command: 0x4010, status: 0x0143
    {1}[Hardware Error]:   device_id: 0000:00:02.2
    {1}[Hardware Error]:   slot: 0
    {1}[Hardware Error]:   secondary_bus: 0x04
    {1}[Hardware Error]:   vendor_id: 0x8086, device_id: 0x2f06
    {1}[Hardware Error]:   class_code: 000604
    {1}[Hardware Error]:   bridge: secondary_status: 0x2000, control: 0x0003
    {1}[Hardware Error]:   aer_uncor_status: 0x00100000, aer_uncor_mask: 0x00000000
    {1}[Hardware Error]:   aer_uncor_severity: 0x00062030
    {1}[Hardware Error]:   TLP Header: 40000018 040000ff 791f4080 00000000
[hw error repeats]
    Kernel panic - not syncing: Fatal hardware error!
    CPU: 0 PID: 2189 Comm: reboot Kdump: loaded Not tainted 5.6.x-blabla #1
    Hardware name: HP ProLiant DL380 Gen9/ProLiant DL380 Gen9, BIOS P89 05/05/2017

Fix the mlx4 driver.

This is a very similar problem to what had been fixed in:
commit 0d98ba8d ("scsi: hpsa: disable device during shutdown")
to address https://bugzilla.kernel.org/show_bug.cgi?id=199779.

Fixes: 2ba5fbd6 ("net/mlx4_core: Handle AER flow properly")
Reported-by: Jake Lawrence <lawja@fb.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>