tcp: Fix data-races around sysctl_tcp_max_reordering.

stable inclusion
from stable-v4.19.254
commit 5e38cee24f19d19280c68f1ac8bf6790d607f60a
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5Q0SQ


CVE: NA

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

[ Upstream commit a11e5b3e7a59fde1a90b0eaeaa82320495cf8cae ]

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

Fixes: dca145ff ("tcp: allow for bigger reordering level")
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: Yongqiang Liu <liuyongqiang13@huawei.com>