LXD fails to create VM with QEMU 7.2.0: "../../net/net.c:1106: net_client_init1: Assertion `nc' failed."
Description of problem:
Beginning with QEMU 7.2.0, LXD is unable to launch virtual machines using the default network profile, which breaks the out-of-box experience if a user wishes to create a virtual machine. This worked correctly with QEMU 7.1.0.

Multiple users across different Linux distributions are reporting this issue:
- https://discuss.linuxcontainers.org/t/failed-adding-nic-netdev-monitor-is-disconnected/15946
- https://forums.gentoo.org/viewtopic-p-8774212.html
- https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1030365

```
gibmat@tharkun:~$ lxc launch images:debian/sid debian-sid-vm --vm
Creating debian-sid-vm
Starting debian-sid-vm                        
Error: Failed setting up device via monitor: Failed setting up device "eth0": Failed adding NIC netdev: Monitor is disconnected
Try `lxc info --show-log local:debian-sid-vm` for more info
gibmat@tharkun:~$ lxc info --show-log local:debian-sid-vm
Name: debian-sid-vm
Status: STOPPED
Type: virtual-machine
Architecture: x86_64
Created: 2023/02/10 23:47 UTC

Log:

warning: tap: open vhost char device failed: Permission denied
warning: tap: open vhost char device failed: Permission denied
qemu-system-x86_64: ../../net/net.c:1106: net_client_init1: Assertion `nc' failed.

```

```
gibmat@tharkun:~$ qemu-system-x86_64 --version
QEMU emulator version 7.2.0 (Debian 1:7.2+dfsg-2)
Copyright (c) 2003-2022 Fabrice Bellard and the QEMU Project developers
gibmat@tharkun:~$ lxc version
Client version: 5.0.2
Server version: 5.0.2
```
Steps to reproduce:
1. Install LXD and QEMU 7.2.0
2. `lxc launch images:debian/sid debian-sid-vm --vm`
  - This will fail as reported above
3. Downgrade to QEMU 7.1.0 (such as from https://snapshot.debian.org/package/qemu/1%3A7.1%2Bdfsg-2/)
4. `lxc launch images:debian/sid debian-sid-vm --vm`
  - Now VM creation is successful
    ```
    gibmat@tharkun:~$ lxc launch images:debian/sid debian-sid-vm --vm
    Creating debian-sid-vm
    Starting debian-sid-vm
    gibmat@tharkun:~$ lxc list
    +---------------+---------+------+-----------------------------------------------+-----------------+-----------+
    |     NAME      |  STATE  | IPV4 |                     IPV6                      |      TYPE       | SNAPSHOTS |
    +---------------+---------+------+-----------------------------------------------+-----------------+-----------+
    | debian-sid-vm | RUNNING |      | fd42:ea61:feb4:55ef:216:3eff:feb8:2e8c (eth0) | VIRTUAL-MACHINE | 0         |
    +---------------+---------+------+-----------------------------------------------+-----------------+-----------+
    gibmat@tharkun:~$ lxc info --show-log local:debian-sid-vm
    Name: debian-sid-vm
    Status: RUNNING
    Type: virtual-machine
    Architecture: x86_64
    PID: 2502
    Created: 2023/02/11 15:08 UTC
    Last Used: 2023/02/11 15:08 UTC
    
    Resources:
      Processes: -1
      Network usage:
        eth0:
          Type: broadcast
          State: UP
          Host interface: tap5efa7582
          MAC address: 00:16:3e:b8:2e:8c
          MTU: 1500
          Bytes received: 3.13kB
          Bytes sent: 164B
          Packets received: 12
          Packets sent: 2
          IP addresses:
            inet6: fd42:ea61:feb4:55ef:216:3eff:feb8:2e8c/64 (global)
    
    Log:
    
    warning: tap: open vhost char device failed: Permission denied
    warning: tap: open vhost char device failed: Permission denied
    
    gibmat@tharkun:~$ qemu-system-x86_64 --version
    QEMU emulator version 7.1.0 (Debian 1:7.1+dfsg-2+b3)
    Copyright (c) 2003-2022 Fabrice Bellard and the QEMU Project developers
    ```