icmp: Fix data-races around sysctl_icmp_echo_enable_probe.

icmp: Fix data-races around sysctl_icmp_echo_enable_probe.

[ Upstream commit f81929d7bae00e78b813879fac8978b59538a513 ]

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

Fixes: 72aea1cc9c46 ("icmp: add response to RFC 8335 PROBE messages")
Fixes: 2f400e428b52 ("ipv6: ICMPV6: add response to ICMPV6 RFC 8335 PROBE messages")
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>