netrom: Fix a data-race around sysctl_netrom_transport_maximum_tries

stable inclusion
from stable-v5.10.213
commit 34a164d2448264b62af82bc0af3d2c83d12d38ac
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/I9Q94J
CVE: CVE-2024-27426

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=34a164d2448264b62af82bc0af3d2c83d12d38ac



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

[ Upstream commit e799299aafed417cc1f32adccb2a0e5268b3f6d5 ]

We need to protect the reader reading the sysctl value because the
value can be changed concurrently.

Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Signed-off-by: Jason Xing <kernelxing@tencent.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Wang Hai <wanghai38@huawei.com>
Signed-off-by: Xiongfeng Wang <wangxiongfeng2@huawei.com>