fix 'default' alias not added to interface specified by network_interface

[kevinschoonover]

closes #18097

consider the following config.hcl

# config.hcl
client {
  network_interface = "tailscale0"

  host_network "tailscale" {
    interface = "tailscale0"
  }

  host_network "public" {
    interface = "wlan0"
  }
}

whenever you would schedule the following job

# job.hcl
job "docs" {
  datacenters = ["dc1"]

  group "example" {
    network {
      port "http" {}
    }
    task "server" {
      driver = "docker"

      config {
        image = "hashicorp/http-echo"
        ports = ["http"]
        args = [
          "-listen",
          ":5678",
          "-text",
          "hello world",
        ]
      }
    }
  }
}

you would see * Constraint "missing host network \"default\" for port \"http\"": 1 nodes excluded by filter because the 'default' host_network alias is being replaces with 'tailscale'. The follow PR appends the 'default' alias regardless to the addresses specified by network_interface.

[tgross]

LGTM! Nice work on this @kevinschoonover!

Two things:

• Can you run make cl here to add a changelog entry?
• Can you rebase on main? We accidentally landed a change in main that's breaking tests, which I've fixed in scheduler: fix panic in render_templates destructive update check #18100 but you don't have on your branch.

[tgross]

LGTM! This will ship in the next Nomad 1.6.x release and get backported to 1.5.x and 1.4.x