network: Only the first nameserver in resolv.conf is ever used

## Bug Report

**Describe the bug**
Given two `nameserver` records in /etc/resolv.conf, fluent-bit doesn't appear to ever use the second record. In particular, when the first record is unavailable (connection refused), fluent-bit simply gives up and errors.

**To Reproduce**
- Configure two DNS servers in resolv.conf (say 127.0.0.1 and a real value)
- Shut down the first one
```
[2022/04/11 19:00:36] [ warn] [net] getaddrinfo(host='example.com', err=12): Timeout while contacting DNS servers
```

**Expected behavior**
I would expect the application to fail-over and attempt resolution against the second nameserver entry.

**Screenshots**
n/a

**Your Environment**

* Version used: 1.8.15 and 1.9.0
* Configuration:
```
[OUTPUT]
Name es
Match journal.*
Host elk.example.com
Port 443
Index logs-journal
Aws_Auth On
Aws_Region us-east-1
Tls On
```
* Environment name and version (e.g. Kubernetes? What version?): EC2 and ECS Fargate
* Server type and version: n/a
* Operating System and version: CentOS 7
* Filters and plugins: n/a

This has been observed in both the td-agent-bit packages (1.9.0) and the aws/aws-for-fluent-bit images (1.8.15).

**Additional context**
We set `127.0.0.1` as our instances have local caching daemons running (dnsmasq). Fluent-bit does not appear to gracefully failover the DNS if the primary resolver is offline or net yet started.

We've observed `v1.8.1` *does not* exhibit this behavior. I'm guessing this is the result of changes in `v1.8.5`, but I have not bisected the releases to verify only skimmed the release notes.