Make sure that del_timer succeeds and removes an entry from the list. Currently
sending the LOCATION UPDATING REJECT from within the timer will not remove the
list element as ->active gets set to 0 in the timer updating before calling the
callback. Fix the segfault and allow the timer to be removed from within its
own callback.
One can use add_timer or schedule_timer to add a timer. After
the timeout time has been reached the callback will be called.
One can call add_time/schedule_timer and del_timer from within
the callback.