This allows using WPA Supplicant "standalone" without an additional
network manager. The default configuration is unchanged.
* gnu/services/networking.scm (<wpa-supplicant-configuration>): New record type.
(wpa-supplicant-shepherd-service): Pass configuration records to the daemon.
(wpa-supplicant-service-type): Adjust accordingly.
* doc/guix.texi (Networking Services): Document the new service type.