ax25: Fix reference count leak issue of net_device

mainline inclusion
from mainline-v6.10-rc1
commit 36e56b1b002bb26440403053f19f9e1a8bc075b2
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/IA6SG4
CVE: CVE-2024-38554

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=36e56b1b002bb26440403053f19f9e1a8bc075b2



--------------------------------

There is a reference count leak issue of the object "net_device" in
ax25_dev_device_down(). When the ax25 device is shutting down, the
ax25_dev_device_down() drops the reference count of net_device one
or zero times depending on if we goto unlock_put or not, which will
cause memory leak.

In order to solve the above issue, decrease the reference count of
net_device after dev->ax25_ptr is set to null.

Fixes: d01ffb9e ("ax25: add refcount in ax25_dev to avoid UAF bugs")
Suggested-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
Reviewed-by: Dan Carpenter <dan.carpenter@linaro.org>
Link: https://lore.kernel.org/r/7ce3b23a40d9084657ba1125432f0ecc380cbc80.1715247018.git.duoming@zju.edu.cn


Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Conflicts:
	net/ax25/ax25_dev.c
[The conflict occurs because the commit a968c799("ax25: merge repeat
codes in ax25_dev_device_down()") and a7d6e36b9ad0("ax25: Use kernel
universal linked list to implement ax25_dev_list") are not merged]
Signed-off-by: Zhengchao Shao <shaozhengchao@huawei.com>