docs/naming: Interval used as timeout?

In https://github.com/hashicorp/memberlist/blob/1a62499c21db33d57691001d5e08a71ec857b18f/state.go#L270-L273

```go
// Send a ping to the node. If this node looks like it's suspect or dead,
// also tack on a suspect message so that it has a chance to refute as
// soon as possible.
deadline := sent.Add(probeInterval)
```

something called `interval` is used as a timeout, which is quite confusing.

And the docs at https://www.consul.io/docs/agent/options.html#probe_interval say:

> `probe_interval` - The interval between random node probes. Setting this lower (more frequent) will cause the cluster to detect failed nodes more quickly at the expense of increased bandwidth usage. The default is 1s.

No indication that this changes the timeout in addition to the _rate_ at which the check is done.

It gets more confusing given that there actually is a setting [`probe_timeout`](https://www.consul.io/docs/agent/options.html#probe_timeout), but that one isn't used as a timeout.

* Should the docs be improved to indicate that this "interval" actually also controls a timeout?
* Or is this a bug, and it should be `deadline := sent.Add(m.awareness.ScaleTimeout(m.config.ProbeTimeout)` instead?