Where we're running with systemd-logind integration we have to assume that
logind may change the KDSKBMODE while we're VT-switched away. If that happens
and we return, our keyboard input may leak to the console.

Fix this by always calling K_OFF/K_RAW on VT switch back. We don't update
the current settings though, so on shutdown we will restore to settings we had
on init. Given the assumption is that if something messes with our vt, it will
mess again anyway, it's not worth the bother.

Fixes #857

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>