ⓘ Treat Linux active virtual interfaces as secondary IP addresses instead of independent links, fixing alias parsing, hiding invalid status controls, rejecting down-state creation, and removing existing aliases with ip addr del when needed.
Reproduce path:
Example repro before this fix:
1. Go to **Network Configuration → Network Interfaces → Active Now**.
2. Click **Add a new interface**.
3. Enter:
```text
Name: enp0s5:1
IPv4 address: 10.211.55.21
Netmask: 255.255.255.0
Status: Down
```
4. Click **Create**.
Before the fix, Webmin could still create the alias or handle it inconsistently, because `enp0s5:1` is not a real link that can be “down”. It is just an extra IP address on `enp0s5`.
Expected after the fix:
- The UI should not offer `Status` for active virtual aliases.
- If someone submits `up=0` manually anyway, Webmin rejects it with:
`Virtual interfaces cannot be created with down status`
- If an existing active virtual alias is saved as down through lower-level code, Webmin removes the IP using something like:
```bash
ip addr del 10.211.55.21/24 dev enp0s5
```
