To write the init script.
And fix the JetKVM detection to work during early boot while the filesystem
and modules are still being loaded; it wasn't being detected on early boot
and then tailscaled was failing to start because it didn't know it was on JetKVM
and didn't modprobe tun.
Updates #16524
Change-Id: I0524ca3abd7ace68a69af96aab4175d32c07e116
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>