This field can be read locklessly from do_tcp_getsockopt()

Fixes: dca43c75 ("tcp: Add TCP_USER_TIMEOUT socket option.")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20230719212857.3943972-11-edumazet@google.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>