Add netstat plugin to Linux monitoring template

**Is your template request related to a problem? Please describe.**

Not related to a problem. But, the netstat plugin isn't listed in the telegraf config for the Linux template file https://github.com/influxdata/community-templates/blob/master/linux_system/linux_system.yml.

Seems like it should be added, unless I'm missing something.

**Describe the solution you'd like**

Assuming netstat plugin works for Linux systems and adds useful metrics, please add to the Linux template.

Start with linux_system/linux_system.yml and inspect how existing input plugins are configured. Verify that the netstat plugin supports Linux and provides useful metrics, then determine whether adding it to the template is appropriate. Done means the Linux template includes the plugin configuration if that support is confirmed.

Written by the indexing model from the issue text.