TM UI and /api/cache-statuses reports aggregate bandwidth_kbps as 0 unless interfaces are monitored

[rawlinp]

I'm submitting a ...

• bug report

Traffic Control components affected ...

• Traffic Monitor

Current behavior:

In the TM UI, bandwidth is reported as 0 unless the server has interfaces with monitor = true.

The /api/cache-statuses API also has the same issue:

  "odol-atsmid-oshob-01": {
    "type": "MID",
    "load_average": 1.55,
    "query_time_ms": 1939,
    "health_time_ms": 1,
    "stat_time_ms": 1,
    "stat_span_ms": 5819,
    "health_span_ms": 1940,
    "status": "REPORTED - available",
    "status_poller": "health",
    "bandwidth_kbps": 0,
    "bandwidth_capacity_kbps": 1000000,
    "connection_count": 16,
    "ipv4_available": true,
    "ipv6_available": true,
    "combined_available": true,
    "interfaces": {
      "ens3": {
        "status": "available",
        "status_poller": "health",
        "bandwidth_kbps": 266,
        "available": true
      }
    }
  },

As you can see, this host is doing 266 kbps, but it's not showing in the UI or in the bandwidth_kbps field (the aggregate of all interfaces) in this API.

Expected behavior:

The UI and /api/cache-statuses API should report the aggregate bandwidth of a server's interfaces, even if monitor = false.

Minimal reproduction of the problem with instructions:

Open the TM UI and observe what I've described for servers with no monitored interfaces. Then make one or more of those interfaces monitored and observe that the bandwidth starts reporting correctly.

[srijeet0406]

@rawlinp I can take this one