lib: fix thread_cancel_event()

lib: fix thread_cancel_event()

  ospfd was crashing some times on neighbour going down. The cause was that
ospf_nsm_event() was accessing already freed memory in ospf_nbr_delete()
call from ospf_nsm_event().

  What happens is that since commit b5043aab (lib: fix incorrect thread
list...) now a thread can be on the event and ready lists but
thread_cancel_event() doesn't account for that.

* thread.c: (thread_cancel_event) loop on the ready list too to cancel
  pending events.

Signed-off-by: Jorge Boncompte [DTI2] <jorge@dti2.net>
Signed-off-by: David Lamparter <equinox@opensourcerouting.org>