(ITS#4401) assert after deleting persistent syncrepl consumer

[hyc@OpenLDAP.org]

Full_Name: Howard Chu
Version: HEAD, 2.3.xx
OS: 
URL: ftp://ftp.openldap.org/incoming/
Submission from: (NULL) (24.126.120.178)
Submitted by: hyc


If the syncrepl consumer was running in refreshAndPersist mode and the
olcSyncrepl attribute is deleted from the database in cn=config, an assert
failure is triggered in daemon.c on the next incoming connection. This is
because connection_client_stop was not called when tearing down the consumer.