[BUG] FreeBSD 15 have new exit code for netstat

This netstat request in FreeBSD always have error (FreeBSD netstat allow only short flags)

https://github.com/canonical/cloud-init/blob/b5046c4002b14dd6ba7aa12be99a1cf3cdb1c148/cloudinit/netinfo.py#L561

In 14.2 release and early

```
subp.py[DEBUG]: Running command ['netstat', '--route', '--numeric', '--extend'] with allowed return codes [0, 1] (shell=False, capture=True)
subp.py[DEBUG]: Running command ['netstat', '-A', 'inet6', '--route', '--numeric'] with allowed return codes [0, 1] (shell=False, capture=True)
```

But in 15-CURRENT, this broken, exit code netstat 64 now
```
subp.py[DEBUG]: Running command ['netstat', '--route', '--numeric', '--extend'] with allowed return codes [0, 1] (shell=False, capture=True)
2025-05-04 12:23:51,444 - util.py[WARNING]: Route info failed: Unexpected error while running command.
Command: ['netstat', '--route', '--numeric', '--extend']
Exit code: 64
Reason: -
Stdout:
Stderr: netstat: illegal option -- -
...
Traceback (most recent call last):
File "/usr/local/lib/python3.11/site-packages/cloudinit/netinfo.py", line 580, in route_pformat
routes = route_info()
^^^^^^^^^^^^
File "/usr/local/lib/python3.11/site-packages/cloudinit/netinfo.py", line 514, in route_info
(route_out, _err) = subp.subp(
^^^^^^^^^^
File "/usr/local/lib/python3.11/site-packages/cloudinit/subp.py", line 298, in subp
raise ProcessExecutionError(
```