Notify init(8) about new USB terminals. This is used to notify init(8)
about USB serial devices (in particular device-side ones) it might want
to run getty(8) for.
Note that this could be generalized to use "tty*" instead, since in theory
we might hot plug some other tty interface.
Before you ask: init(8) seems to carefully ignore the SIGHUP signal
(which is what "init q" ends up sending) when it's not ready to handle it.