tstest/natlab/vnet: add start of virtual network-based NAT Lab

Updates #13038

Change-Id: I3c74120d73149c1329288621f6474bbbcaa7e1a6
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

cmd/vnet/run-krazy.sh

@@ -0,0 +1,20 @@
+#!/usr/bin/env bash
+
+echo "Type 'C-a c' to enter monitor; q to quit."
+
+set -eux
+qemu-system-x86_64 -M microvm,isa-serial=off \
+    -m 1G \
+    -nodefaults -no-user-config -nographic \
+    -kernel $HOME/src/github.com/tailscale/gokrazy-kernel/vmlinuz \
+    -append "console=hvc0 root=PARTUUID=60c24cc1-f3f9-427a-8199-dd02023b0001/PARTNROFF=1 ro init=/gokrazy/init panic=10 oops=panic pci=off nousb tsc=unstable clocksource=hpet tailscale-tta=1" \
+    -drive id=blk0,file=$HOME/src/tailscale.com/gokrazy/tsapp.img,format=raw \
+    -device virtio-blk-device,drive=blk0 \
+    -netdev stream,id=net0,addr.type=unix,addr.path=/tmp/qemu.sock \
+    -device virtio-serial-device \
+    -device virtio-net-device,netdev=net0,mac=52:cc:cc:cc:cc:00 \
+    -chardev stdio,id=virtiocon0,mux=on \
+    -device virtconsole,chardev=virtiocon0 \
+    -mon chardev=virtiocon0,mode=readline \
+    -audio none
+