When a devlink port is unregistered, its type is expected to be unset or
otherwise a WARNING is generated [1]. This was supposed to be handled by
cited commit by clearing the type upon 'NETDEV_PRE_UNINIT'.

The assumption was that no other events can be generated for the netdev
after this event, but this proved to be wrong. After the event is
generated, netdev_wait_allrefs_any() will rebroadcast a
'NETDEV_UNREGISTER' until the netdev's reference count drops to 1. This
causes devlink to set the port type back to Ethernet.

Fix by only setting and clearing the port type upon 'NETDEV_POST_INIT'
and 'NETDEV_PRE_UNINIT', respectively. For all other events, preserve
the port type.

[1]
WARNING: CPU: 0 PID: 11 at net/core/devlink.c:9998 devl_port_unregister+0x2f6/0x390 net/core/devlink.c:9998
Modules linked in:
CPU: 1 PID: 11 Comm: kworker/u4:1 Not tainted 6.1.0-rc3-next-20221107-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022
Workqueue: netns cleanup_net
RIP: 0010:devl_port_unregister+0x2f6/0x390 net/core/devlink.c:9998
[...]
Call Trace:
 <TASK>
 __nsim_dev_port_del+0x1bb/0x240 drivers/net/netdevsim/dev.c:1433
 nsim_dev_port_del_all drivers/net/netdevsim/dev.c:1443 [inline]
 nsim_dev_reload_destroy+0x171/0x510 drivers/net/netdevsim/dev.c:1660
 nsim_dev_reload_down+0x6b/0xd0 drivers/net/netdevsim/dev.c:968
 devlink_reload+0x1c2/0x6b0 net/core/devlink.c:4501
 devlink_pernet_pre_exit+0x104/0x1c0 net/core/devlink.c:12609
 ops_pre_exit_list net/core/net_namespace.c:159 [inline]
 cleanup_net+0x451/0xb10 net/core/net_namespace.c:594
 process_one_work+0x9bf/0x1710 kernel/workqueue.c:2289
 worker_thread+0x665/0x1080 kernel/workqueue.c:2436
 kthread+0x2e4/0x3a0 kernel/kthread.c:376
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:308
 </TASK>

Fixes: 02a68a47 ("net: devlink: track netdev with devlink_port assigned")
Reported-by: syzbot+85e47e1a08b3e159b159@syzkaller.appspotmail.com
Reported-by: syzbot+c2ca18f0fccdd1f09c66@syzkaller.appspotmail.com
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Link: https://lore.kernel.org/r/20221110085150.520800-1-idosch@nvidia.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>