tcp: Fix a data-race around sysctl_tcp_min_rtt_wlen.

stable inclusion
from stable-v5.10.135
commit 83edb788e69a0d5ad40ba5be6a60d6db265d0500
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5ZWFM

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=83edb788e69a0d5ad40ba5be6a60d6db265d0500



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[ Upstream commit 1330ffac ]

While reading sysctl_tcp_min_rtt_wlen, it can be changed concurrently.
Thus, we need to add READ_ONCE() to its reader.

Fixes: f6722583 ("tcp: track min RTT using windowed min-filter")
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>
Reviewed-by: Wei Li <liwei391@huawei.com>