A [netdev] in a -readconfig file does not stop QEMU from adding its
default NIC, so the guests had a second user-mode network without the
SSH port forward. Both NICs got 10.0.2.15 over DHCP, and SSH only worked
on boots where the forwarded NIC won the race for the default route.
Removing the default NIC shifts the other PCI devices down one slot, so
existing VMs may need their UEFI variable store reset to boot again.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
