tcp: Fix a data-race around sysctl_tcp_invalid_ratelimit.

stable inclusion
from stable-v4.19.255
commit 69eab4c78d7a366d75de3d07e0a4a9e7c81291c1
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5Q0SQ


CVE: NA

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

[ Upstream commit 2afdbe7b8de84c28e219073a6661080e1b3ded48 ]

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

Fixes: 032ee423 ("tcp: helpers to mitigate ACK loops by rate-limiting out-of-window dupacks")
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>