net: annotate lockless accesses to sk->sk_max_ack_backlog

[ Upstream commit 099ecf59f05b5f30f42ebac0ab8cb94f9b18c90c ]

sk->sk_max_ack_backlog can be read without any lock being held
at least in TCP/DCCP cases.

We need to use READ_ONCE()/WRITE_ONCE() to avoid load/store tearing
and/or potential KCSAN warnings.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Stable-dep-of: 4d5c70e6155d ("sctp: ensure sk_state is set to CLOSED if hashing fails in sctp_listen_start")
Signed-off-by: Sasha Levin <sashal@kernel.org>