Use correct order of arguments for shutdown(2).

Use correct order of arguments for shutdown(2).

Luckily routesock would never be <= 2 so shutdown would always failing
with EINVAL and not shutting down random other sockets.
The kernel was just uselessly piling up route messages that we were
never reading.

This mistake first showed up in slaacd(8) and then was copied to the
other daemons.

Reported & fixed by Josiah Frentsos (jfrent at tilde.team), thanks!
OK kn