wifi: virt_wifi: remove SET_NETDEV_DEV to avoid use-after-free

In the Linux kernel, the following vulnerability has been resolved:

wifi: virt_wifi: remove SET_NETDEV_DEV to avoid use-after-free

Currently we execute `SET_NETDEV_DEV(dev, &priv->lowerdev->dev)` for
the virt_wifi net devices. However, unregistering a virt_wifi device in
netdev_run_todo() can happen together with the device referenced by
SET_NETDEV_DEV().

It can result in use-after-free during the ethtool operations performed
on a virt_wifi device that is currently being unregistered. Such a net
device can have the `dev.parent` field pointing to the freed memory,
but ethnl_ops_begin() calls `pm_runtime_get_sync(dev->dev.parent)`.

Let's remove SET_NETDEV_DEV for virt_wifi to avoid bugs like this:

==================================================================
BUG: KASAN: slab-use-after-free in __pm_runtime_resume+0xe2/0xf0
Read of size 2 at addr ffff88810cfc46f8 by task pm/606

Call Trace:
<TASK>
dump_stack_lvl+0x4d/0x70
print_report+0x170/0x4f3
? __pfx__raw_spin_lock_irqsave+0x10/0x10
kasan_report+0xda/0x110
? __pm_runtime_resume+0xe2/0xf0
? __pm_runtime_resume+0xe2/0xf0
__pm_runtime_resume+0xe2/0xf0
ethnl_ops_begin+0x49/0x270
ethnl_set_features+0x23c/0xab0
? __pfx_ethnl_set_features+0x10/0x10
? kvm_sched_clock_read+0x11/0x20
? local_clock_noinstr+0xf/0xf0
? local_clock+0x10/0x30
? kasan_save_track+0x25/0x60
? __kasan_kmalloc+0x7f/0x90
? genl_family_rcv_msg_attrs_parse.isra.0+0x150/0x2c0
genl_family_rcv_msg_doit+0x1e7/0x2c0
? __pfx_genl_family_rcv_msg_doit+0x10/0x10
? __pfx_cred_has_capability.isra.0+0x10/0x10
? stack_trace_save+0x8e/0xc0
genl_rcv_msg+0x411/0x660
? __pfx_genl_rcv_msg+0x10/0x10
? __pfx_ethnl_set_features+0x10/0x10
netlink_rcv_skb+0x121/0x380
? __pfx_genl_rcv_msg+0x10/0x10
? __pfx_netlink_rcv_skb+0x10/0x10
? __pfx_down_read+0x10/0x10
genl_rcv+0x23/0x30
netlink_unicast+0x60f/0x830
? __pfx_netlink_unicast+0x10/0x10
? __pfx___alloc_skb+0x10/0x10
netlink_sendmsg+0x6ea/0xbc0
? __pfx_netlink_sendmsg+0x10/0x10
? __futex_queue+0x10b/0x1f0
____sys_sendmsg+0x7a2/0x950
? copy_msghdr_from_user+0x26b/0x430
? __pfx_____sys_sendmsg+0x10/0x10
? __pfx_copy_msghdr_from_user+0x10/0x10
___sys_sendmsg+0xf8/0x180
? __pfx____sys_sendmsg+0x10/0x10
? __pfx_futex_wait+0x10/0x10
? fdget+0x2e4/0x4a0
__sys_sendmsg+0x11f/0x1c0
? __pfx___sys_sendmsg+0x10/0x10
do_syscall_64+0xe2/0x570
? exc_page_fault+0x66/0xb0
entry_SYSCALL_64_after_hwframe+0x77/0x7f
</TASK>

This fix may be combined with another one in the ethtool subsystem:
https://lore.kernel.org/all/20260322075917.254874-1-alex.popov@linux.com/T/#u