PR12309 part 1, use atomic_t for delayed_work state signaling

PR12309 part 1, use atomic_t for delayed_work state signaling

There was a possible race condition between multiple processes opening
the transport .ctl file concurrently.

* runtime/transport/transport.h (_stp_ctl_attached): Become atomic_t.
* runtime/transport/transport.c (_stp_attach, _stp_detach):
  Stop messing with it.
* runtime/transport/control.c (_stp_ctl_open|close_cmd): Use atomic_t
  and reorder logic to defeat race condition.