Network mode: mirrored - IPv4 broken with CLAT

### Windows Version

Microsoft Windows [Version 10.0.26220.9223]

### WSL Version

2.9.4.0

### Are you using WSL 1 or WSL 2?

- [x] WSL 2
- [ ] WSL 1

### Kernel Version

6.18.35.2-1

### Distro Version

Debian 13

### Other Software

_No response_

### Repro Steps

- Host has WinCLAT enabled.
- CLAT is active
- WSL VM has Networking mode `mirrored`

No IPv4 connectivity through the CLAT.

### Expected Behavior

- Connectivity through the CLAT like the host

### Actual Behavior

- No connectivity through the CLAT
- route is present

```
ping 1.1.1.1
PING 1.1.1.1 (1.1.1.1) 56(84) bytes of data.
From 192.0.0.1 icmp_seq=1 Destination Host Unreachable
ping: sendmsg: No route to host
From 192.0.0.1 icmp_seq=2 Destination Host Unreachable
From 192.0.0.1 icmp_seq=3 Destination Host Unreachable
^C
--- 1.1.1.1 ping statistics ---
5 packets transmitted, 0 received, +3 errors, 100% packet loss, time 4091ms
pipe 3
```

In Debian:
```
ip -4 route
default via 192.0.0.0 dev eth2 proto kernel metric 281
192.0.0.0 dev eth2 proto kernel scope link metric 281
```

### Diagnostic Logs

_No response_

Start by reproducing the issue with WinCLAT active, WSL 2 mirrored networking, and Debian 13, then inspect the reported IPv4 route and diagnostic behavior. The fix is complete when WSL can reach IPv4 destinations through CLAT in mirrored mode, matching the host's connectivity.

Written by the indexing model from the issue text.