Restore the `dev.tty.legacy_tiocsti` check

Restore the `dev.tty.legacy_tiocsti` check

The kernel documentations says:
```
Historically the kernel has allowed TIOCSTI, which will push
characters into a controlling TTY. This continues to be used
as a malicious privilege escalation mechanism, and provides no
meaningful real-world utility any more. Its use is considered
a dangerous legacy operation, and can be disabled on most
systems.
```
https://elixir.bootlin.com/linux/v6.8.8/source/drivers/tty/Kconfig#L152

In other words, not having the `dev.tty.legacy_tiocsti` sysctl means that
the dangerous functionality is enabled by default.