If LOCALSTATEDIR is inaccessible, store the pid and socket files in the configuration...

If LOCALSTATEDIR is inaccessible, store the pid and socket files in the configuration directory.

The compile time local state directory is usually /var or
/usr/local/var. If this is not accessible for some reason, for example
because someone ./configured tinc without --localstatedir and
/usr/local/var does not exist, or if tinc is started by a non-root user,
then tinc will fall back to the directory where tinc.conf is stored.
A warning is logged when this happens.