ip: Fix data-races around sysctl_ip_no_pmtu_disc.

mainline inclusion
from mainline-v5.19-rc8
commit 0968d2a4
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I8P5HO
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=0968d2a441bf6afb551fd99e60fa65ed67068963



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

Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Conflicts:
	net/ipv4/icmp.c
	net/ipv6/af_inet6.c
	net/xfrm/xfrm_state.c

Signed-off-by: Zhengchao Shao <shaozhengchao@huawei.com>