[net] Question about ipvs->sysctl_sync_threshold and READ_ONCE

[Zijie Zhao <zzjas98@xxxxxxxxx>]

Dear IPVS maintainers,

We encountered an unusual usage of sysctl parameter while analyzing 
kernel source code.

In include/net/ip_vs.h, line 1062 - 1070:

```
static inline int sysctl_sync_threshold(struct netns_ipvs *ipvs)
{
        return ipvs->sysctl_sync_threshold[0];
}

static inline int sysctl_sync_period(struct netns_ipvs *ipvs)
{
        return READ_ONCE(ipvs->sysctl_sync_threshold[1]);
}
```

Here, sysctl_sync_threshold[1] is accessed behind `READ_ONCE`, but 
sysctl_sync_threshold[0] is not. Should sysctl_sync_threshold[0] also be 
guarded by `READ_ONCE`?
Please kindly let us know if we missed any key information and this is 
actually intended. We appreciate your information and time! Thanks!

Links to the code:
https://elixir.bootlin.com/linux/v6.8.1/source/include/net/ip_vs.h#L1064
https://elixir.bootlin.com/linux/v6.8.1/source/include/net/ip_vs.h#L1069

Best,
Zijie