rego-tunnel: parameterize net + add DHCP static lease

apps/rego-tunnel/build/start-vm.sh

@@ -23,6 +23,8 @@ fi
 # Wait for network setup
 sleep 2
 
+TAP_NAME="${TAP_NAME:-tap0}"
+
 exec qemu-system-x86_64 \
 	-enable-kvm \
 	-cpu host \
@@ -31,7 +33,7 @@ exec qemu-system-x86_64 \
 	-hda /vm/linux-vm.qcow2 \
 	-fsdev local,id=fsdev0,path=/shared,security_model=none,multidevs=remap \
 	-device virtio-9p-pci,fsdev=fsdev0,mount_tag=shared \
-	-netdev tap,id=net0,ifname=tap0,script=no,downscript=no \
+	-netdev tap,id=net0,ifname="$TAP_NAME",script=no,downscript=no \
 	-device virtio-net-pci,netdev=net0,mac=52:54:00:12:34:56 \
 	-vnc :0 \
 	-vga virtio \