Need to Configure VintageNet `:internet_host` setting

[This line](https://github.com/nerves-networking/vintage_net/blob/2fc6f251069aa0ae283524aed6714991c0137773/lib/vintage_net/interface/internet_tester.ex#L26) pings an IP address (can't be a hostname) to check if the device is online. The current value is `1.1.1.1` (CloudFlare DNS host). If this is not available (ie: blocked by local policy), VintageNet will start creating logs that say the device is offline (though it isn't).