Incorrect Source IP address

_Splunk plugin v0.10.0, Fluentd-elasticsearch v2.2.0_

We've got the following section in our `output.conf`:

```

@type copy

@id elasticsearch
@type elasticsearch
@log_level info
type_name fluentd
include_tag_key true
host elasticsearch-logging
port 9200
logstash_format true


@type splunk_tcp
host 1.2.3.4
port 10524
format json
flush_interval 10s

```

On the splunk side, the _source_ IP address is the same address listed as _host_ in the `output.conf`.

What am I doing wrong?

## Splunk Excerpt
```
Jun 17 14:38:55 1.2.3.4
{
"time":1560796725,
"log":"2019-06-17 18:38:45.952 [INFO][77] ipsets.go 253: Resyncing ipsets with dataplane. family=\"inet\"\n",
"stream":"stdout",
"docker": {
"container_id":"xxx"
},
"kubernetes": {
"container_name":"calico-node",
"namespace_name":"kube-system",
"pod_name":"calico-node-sblhz",
"container_image":"quay.io/calico/node:v3.1.3",
"container_image_id":"docker-pullable://quay.io/calico/node@sha256:xxx",
"pod_id":"xxx",
"labels": {
"controller-revision-hash":"3519718735",
"k8s-app":"calico-node",
"pod-template-generation":"1"
},
"host":"splunk-4-k8s-node-nf-1",
"master_url":"https://10.3.0.1:443/api",
"namespace_id":"0a525f10-8e0e-11e9-b699-fa163e2c9676"
}
}
```