Attach multiple network interfaces (multiple TAPs) to a single Firecracker microVM and control guest-side device naming

Documented steps

1. Each NIC is a separate network-interfaces/{id} resource pointing at its own host TAP: PUT /network-interfaces/my_net0 {host_dev_name:tap0}, PUT /network-interfaces/my_net1 {host_dev_name:tap1}
2. iface_id is a Firecracker-internal management label only; the name the interface gets in the guest (eth0, eth1, ...) is decided by the guest kernel, not by Firecracker
3. Set guest_mac explicitly if the guest/rootfs expects a specific MAC-to-IP mapping (e.g. 06:00:AC:10:00:02 for the default 172.16.0.2); otherwise omit it and the guest generates a random MAC
4. Create and NAT/bridge each host TAP separately (ip tuntap add tap1 mode tap; give each its own /30 subnet and masquerade/forward rules) - Firecracker supports only the TUN/TAP backend with no multi-queue
5. Configure routing inside the guest per interface (ip addr add / ip link set up / ip route) or pass kernel ip= boot args to automate it