vhost-user-test outputs scary messages
Description of problem:
The qos-test seems to output failure messages when run in verbose mode, see e.g.:

https://gitlab.com/qemu-project/qemu/-/jobs/3340919275#L5615

```
――――――――――――――――――――――――――――――――――――― ✀  ―――――――――――――――――――――――――――――――――――――
stderr:
qemu-system-aarch64: Failed to set msg fds.
qemu-system-aarch64: vhost VQ 0 ring restore failed: -22: Invalid argument (22)
qemu-system-aarch64: Failed to set msg fds.
qemu-system-aarch64: vhost_set_vring_endian failed: Invalid argument (22)
qemu-system-aarch64: Failed to set msg fds.
qemu-system-aarch64: vhost VQ 1 ring restore failed: -22: Invalid argument (22)
qemu-system-aarch64: Failed to set msg fds.
qemu-system-aarch64: vhost_set_vring_endian failed: Invalid argument (22)
qemu-system-aarch64: -chardev socket,id=chr-reconnect,path=/tmp/vhost-test-9B51V1/reconnect.sock,server=on: info: QEMU waiting for connection on: disconnected:unix:/tmp/vhost-test-9B51V1/reconnect.sock,server=on
qemu-system-aarch64: Failed to set msg fds.
qemu-system-aarch64: vhost VQ 0 ring restore failed: -22: Invalid argument (22)
qemu-system-aarch64: Failed to set msg fds.
qemu-system-aarch64: vhost_set_vring_endian failed: Invalid argument (22)
qemu-system-aarch64: Failed to set msg fds.
qemu-system-aarch64: vhost VQ 1 ring restore failed: -22: Invalid argument (22)
qemu-system-aarch64: Failed to set msg fds.
qemu-system-aarch64: vhost_set_vring_endian failed: Invalid argument (22)
qemu-system-aarch64: -chardev socket,id=chr-connect-fail,path=/tmp/vhost-test-49UUV1/connect-fail.sock,server=on: info: QEMU waiting for connection on: disconnected:unix:/tmp/vhost-test-49UUV1/connect-fail.sock,server=on
qemu-system-aarch64: -netdev vhost-user,id=hs0,chardev=chr-connect-fail,vhostforce=on: Failed to read msg header. Read 0 instead of 12. Original request 1.
qemu-system-aarch64: -netdev vhost-user,id=hs0,chardev=chr-connect-fail,vhostforce=on: vhost_backend_init failed: Protocol error
qemu-system-aarch64: -netdev vhost-user,id=hs0,chardev=chr-connect-fail,vhostforce=on: failed to init vhost_net for queue 0
qemu-system-aarch64: -netdev vhost-user,id=hs0,chardev=chr-connect-fail,vhostforce=on: info: QEMU waiting for connection on: disconnected:unix:/tmp/vhost-test-49UUV1/connect-fail.sock,server=on
qemu-system-aarch64: Failed to write msg. Wrote -1 instead of 20.
qemu-system-aarch64: vhost VQ 0 ring restore failed: -22: Invalid argument (22)
qemu-system-aarch64: Failed to set msg fds.
qemu-system-aarch64: vhost_set_vring_endian failed: Invalid argument (22)
qemu-system-aarch64: Failed to set msg fds.
qemu-system-aarch64: vhost VQ 1 ring restore failed: -22: Invalid argument (22)
qemu-system-aarch64: Failed to set msg fds.
qemu-system-aarch64: vhost_set_vring_endian failed: Invalid argument (22)
qemu-system-aarch64: -chardev socket,id=chr-flags-mismatch,path=/tmp/vhost-test-LTKOV1/flags-mismatch.sock,server=on: info: QEMU waiting for connection on: disconnected:unix:/tmp/vhost-test-LTKOV1/flags-mismatch.sock,server=on
qemu-system-aarch64: Failed to write msg. Wrote -1 instead of 52.
qemu-system-aarch64: vhost_set_mem_table failed: Invalid argument (22)
qemu-system-aarch64: unable to start vhost net: 22: falling back on userspace virtio
vhost lacks feature mask 0x40000000 for backend
qemu-system-aarch64: failed to init vhost_net for queue 0
qemu-system-aarch64: Failed to write msg. Wrote -1 instead of 20.
qemu-system-aarch64: vhost_set_vring_num failed: Invalid argument (22)
qemu-system-aarch64: unable to start vhost net: 22: falling back on userspace virtio
qemu-system-aarch64: Failed to set msg fds.
qemu-system-aarch64: vhost VQ 0 ring restore failed: -22: Invalid argument (22)
qemu-system-aarch64: Failed to set msg fds.
qemu-system-aarch64: vhost_set_vring_endian failed: Invalid argument (22)
qemu-system-aarch64: Failed to set msg fds.
qemu-system-aarch64: vhost VQ 1 ring restore failed: -22: Invalid argument (22)
qemu-system-aarch64: Failed to set msg fds.
qemu-system-aarch64: vhost_set_vring_endian failed: Invalid argument (22)
qemu-system-aarch64: Failed to set msg fds.
qemu-system-aarch64: vhost VQ 2 ring restore failed: -22: Invalid argument (22)
qemu-system-aarch64: Failed to set msg fds.
qemu-system-aarch64: vhost_set_vring_endian failed: Invalid argument (22)
qemu-system-aarch64: Failed to set msg fds.
qemu-system-aarch64: vhost VQ 3 ring restore failed: -22: Invalid argument (22)
qemu-system-aarch64: Failed to set msg fds.
qemu-system-aarch64: vhost_set_vring_endian failed: Invalid argument (22)
qemu-system-aarch64: Failed to set msg fds.
qemu-system-aarch64: vhost VQ 0 ring restore failed: -22: Invalid argument (22)
qemu-system-aarch64: Failed to set msg fds.
qemu-system-aarch64: vhost_set_vring_endian failed: Invalid argument (22)
qemu-system-aarch64: Failed to set msg fds.
qemu-system-aarch64: vhost VQ 1 ring restore failed: -22: Invalid argument (22)
qemu-system-aarch64: Failed to set msg fds.
qemu-system-aarch64: vhost_set_vring_endian failed: Invalid argument (22)
qemu-system-aarch64: Failed to set msg fds.
qemu-system-aarch64: vhost VQ 0 ring restore failed: -22: Invalid argument (22)
qemu-system-aarch64: Failed to set msg fds.
qemu-system-aarch64: vhost_set_vring_endian failed: Invalid argument (22)
qemu-system-aarch64: Failed to set msg fds.
qemu-system-aarch64: vhost VQ 1 ring restore failed: -22: Invalid argument (22)
qemu-system-aarch64: Failed to set msg fds.
qemu-system-aarch64: vhost_set_vring_endian failed: Invalid argument (22)
qemu-system-aarch64: Failed to set msg fds.
qemu-system-aarch64: vhost VQ 0 ring restore failed: -22: Invalid argument (22)
qemu-system-aarch64: Failed to set msg fds.
qemu-system-aarch64: vhost VQ 1 ring restore failed: -22: Invalid argument (22)
qemu-system-aarch64: Failed to set msg fds.
qemu-system-aarch64: vhost_set_vring_call failed: Invalid argument (22)
qemu-system-aarch64: Failed to set msg fds.
qemu-system-aarch64: vhost_set_vring_call failed: Invalid argument (22)
――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――
```