Add support for port aggregation (#182)

* Add support for port aggregation

Fixes #142

* Return `*unifi.Device` from `allocateDevice`

* Merge `TestAccDevice_switch_portOverrides` and `TestAccDevice_remove_portOverrides`

* Add tests

Note that only switches with a Broadcom, Microsemi or Nephos chipset support both port mirroring and port aggregation.

```java
package com.ubnt.data;

public class Device extends X implements Sanitizable
{

  // ...

  public int getMaxMirrorSession() {
    int n = 0;
    if (this.getModel() == Model.\u00f8\u00f50000) {
      n = 2;
    }
    else if (this.isBroadcomSwitch() || this.isMicrosemiSwitch() || this.isMediaTekSwitch() || this.isNephosSwitch()) {
      n = 1;
    }
    return this.thisforObject().getInt("max_mirror_sessions", n);
  }

  public int getMaxAggregation() {
    int n = 0;
    if (this.isBroadcomSwitch() || this.isMicrosemiSwitch() || this.isNephosSwitch()) {
      n = 6;
    }
    return this.thisforObject().getInt("max_aggregate_sessions", n);
  }

  // ...

  public boolean isBroadcomSwitch() {
    final Model model = this.getModel();
    return model.getChipset().typeOf(Chipset.\u00f400000) && model.getType() == DeviceType.if;
  }

  public boolean isMicrosemiSwitch() {
    final Model model = this.getModel();
    return model.getChipset().typeOf(Chipset.o00000) && model.getType() == DeviceType.if;
  }

  public boolean isMediaTekSwitch() {
    final Model model = this.getModel();
    return model.getChipset().typeOf(Chipset.\u00d3O0000) && model.getType() == DeviceType.if;
  }

  public boolean isNephosSwitch() {
    final Model model = this.getModel();
    return model.getChipset().typeOf(Chipset.\u00d5O0000) && model.getType() == DeviceType.if;
  }

  // ...

}
```

To extract the list of models that use one of these chipsets I used the following script (executed as `java --class-path path/to/ace.jar main.java`):

```java
import com.ubnt.data.Model;

class UniFiModels {
  public static void main(String[] args) {
    /*
    for (Model model : Model.values()) {
      System.out.printf(
          "Model = %s\nSKU = %s\nType = %s\nFeatures = %s\nChipset = %s\nSysId = %s\nPortNum = %s\n\n",
          model,
          model.getSku(),
          model.getType(),
          model.getFeatures(),
          model.getChipset(),
          model.getSysId(),
          model.getPortNum());
    }
    */

    for (Model model : Model.values()) {
      System.out.printf("%s: %s (%s)\n", model.getChipset(), model, model.getSku());
    }
  }
}

```

---------

Co-authored-by: Joshua Spence <josh@spence.com.au>

examples/resources/unifi_device/resource.tf

@@ -33,4 +33,11 @@ resource "unifi_device" "us_24_poe" {
     name            = "disabled"
     port_profile_id = data.unifi_port_profile.disabled.id
   }
+
+  # port aggregation for ports 11 and 12
+  port_override {
+    number              = 11
+    op_mode             = "aggregate"
+    aggregate_num_ports = 2
+  }
 }