netstat: print route weight

[melifaro]

Summary

Output relative path weight when listing routes in netstat w/ non-display output (e.g json/xml).

Test Plan

8:56 [2] m@devel2 netstat -4rnW --libxo json,pretty
{
  "statistics": {
    "route-information": {
      "route-table": {
        "rt-family": [
          {
            "address-family": "Internet",
            "rt-entry": [
              {
                "destination": "default",
                "gateway": "10.0.0.1",
                "flags": "UGS",
                "flags_pretty": [
                  "up",
                  "gateway",
                  "static"
                ],
                "weight": 1,
                "nhop": 4,
                "mtu": 1500,
                "interface-name": "vtnet0"
              },