Support "services" root config in cfgv4

[Vigilans]

This allows tun to be configured in v4cfg:

  "services": {
    "tun": {
      "name": "tun0",
      "mtu": 1500,
      "tag": "tun",
      "ips": [{ "ip": [198, 18, 0, 0], "prefix": 15 }],
      "routes": [
         { "ip": [0, 0, 0, 0], "prefix": 0 }
         // , { "ip": [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0], "prefix": 0 }
      ],
      "enablePromiscuousMode": true,
      "enableSpoofing": true
    }
  }

Fixes #2541 (comment)

[Losalado]

Great, thanks!

[xiaokangwang]

I think this merge request is ready to be merged. A merge request for its document is welcomed! To process merge request faster, documentation task will no longer be a release blocker.

[Losalado]

It works in my device now.
Many thanks for your job.