The same firmware image may be deployed on either bare metal device or
virtualized platforms (e.g., Proxmox VE).
On bare metal device, `qemu-ga` may still be started even though no
virtio-serial channel is available, resulting in repeated attempts to
access /dev/virtio-ports/org.qemu.guest_agent.0.
This causes continuous service respawning by procd and unnecessary log
spam.
This commit adds a pre-check for /dev/virtio-ports to avoid starting
`qemu-ga` when virtio-serial support is not present.
Signed-off-by: Andy Chiang <AndyChiang_git@outlook.com>
Andy Chiang