Ticket 48040 - preserve the FD when disabling a listener
    
    Bug Description:  Stopping the server when the listener is disabled
                      crashes the serveri becuase we close the listener
                      FD twice.
    
    Fix Description:  When disabling a listener, pass the "preserve fd"
                      flag to ns_job_modify().  This prevents nunc-stans
                      from closing the FD out from underneath us.
    
    https://fedorahosted.org/389/ticket/48040
    
    Reviewed by: rmeggins(Thanks!)