tcp: tcp_moderate_rcvbuf is only used in rx path

tcp: tcp_moderate_rcvbuf is only used in rx path

sysctl_tcp_moderate_rcvbuf is only used from tcp_rcvbuf_grow().

Move it to netns_ipv4_read_rx group.

Remove various CACHELINE_ASSERT_GROUP_SIZE() from netns_ipv4_struct_check(),
as they have no real benefit but cause pain for all changes.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20251119084813.3684576-2-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>