client: Improve initialization of client-state structure

- Split ni_fsm_get_matching_workers() and ni_fsm_mark_matching_workers()
- Introduce new type ni_ifmarker_t to mark specific attributes of
  ifworkers (target_range, persistent)
- get rid of ni_fsm_set_client_state() and move the functionality to
  ni_ifworker_start() - possible due to the above split
- Introduce macro to carefully set control flags like persistent and
  usercontrol