[inputs.ping] Native method gives higher results comparing to exec

Native method gives wrong results comparing to exec mode.

### Relevant telegraf.conf:

```toml
[[inputs.ping]]
urls = [
"host1",
"host2",
"host3",
"host4",
"host5",
]
```

### System info:

Telegraf 1.19.3 (git: HEAD a799489f)
Debian Linux x86_64

### Steps to reproduce:

1. Collect ping data using preferred **native** method
2. Collect ping data using the **exec** method
3. Compare the results

### Expected behavior:

The ping reply time should be at least comparable

### Actual behavior:

Now it look like this

You probably can see on this graph at which time I changed from native to exec :)

### Additional info:

No idea why the ping is collecting the data wrongly in native mode - just guessing:
1. spawning new ping thread overhead?
2. thread's priority?

Start with the inputs.ping native and exec collection paths and reproduce the comparison using the Telegraf configuration shown. Measure where reply times diverge, then verify that native-mode results are comparable to exec-mode results under the same hosts and collection conditions.

Written by the indexing model from the issue text.