fix paragraph in the default Kea configuration files
The following paragraph in the default Kea configuration files is wrong:
// This configuration file contains only DHCPv4 server's configuration.
// If configurations for other Kea services are also included in this file they
// are ignored by the DHCPv4 server.
Specifically, when you try to put additional configurations into the DHCPv4 configuration file, it would spit out an error.