mod_timer — modify a timer's timeout
| int mod_timer ( | struct timer_list * timer, | 
| unsigned long expires ); | 
   mod_timer is a more efficient way to update the expire field of an
   active timer (if the timer is inactive it will be activated)
   
mod_timer(timer, expires) is equivalent to:
del_timer(timer); timer->expires = expires; add_timer(timer);
   Note that if there are multiple unserialized concurrent users of the
   same timer, then mod_timer is the only safe way to modify the timeout,
   since add_timer cannot modify an already running timer.
   
   The function returns whether it has modified a pending timer or not.
   (ie. mod_timer of an inactive timer returns 0, mod_timer of an
   active timer returns 1.)