monitor: use-after-free bugfix
    
    *monitor_kill_service* may create timed event which operates on *svc* and
    therefore *svc* should not be freed right after call of *monitor_kill_sercice*.
    *svc* is supposed to be freed by *mt_svc_restart*.
    
    (cherry picked from commit f89cf190f58f3f5c73758abd0a24974a78cb160b)