services: rsync: Provide a prettier Shepherd inetd service name.

Previously, a default name would be used for transient inetd services,
leading to names such as #{5rjnskb6011jgmfmpgp63jp9mh9nkl20-rsync-3274}#.

* gnu/services/rsync.scm (rsync-shepherd-service): Pass #:service-name-stem.

Change-Id: I4d0a4a01e122c6eeaa85f104b083cf7e8709eac3

gnu/services/rsync.scm

@@ -291,6 +291,7 @@ please use 'modules' instead~%")))
                                        (make-socket-address AF_INET6 IN6ADDR_ANY
                                                             #$port-number)))
                                      '()))
+                           #:service-name-stem "rsync"
                            #:user #$user
                            #:group #$group)
                           (make-forkexec-constructor #$rsync-command