tcp: Fix data-races around sysctl_tcp_no_ssthresh_metrics_save.

stable inclusion
from stable-v5.10.135
commit 2b4b373271e5a39117f520dfa931f2f801f3076f
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=2b4b373271e5a39117f520dfa931f2f801f3076f



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commit ab1ba21b upstream.

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

Fixes: 65e6d901 ("net-tcp: Disable TCP ssthresh metrics cache by default")
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>
Reviewed-by: Wei Li <liwei391@huawei.com>