Fix a logic error that occur when using the timerfd interface

This sequence of events posed a problem

timerfd_timer_open
timerfd_timer_enable_continuous
timerfd_timer_set_rate
timerfd_timer_disable_continuous

The reason was that the timing module was written under the assumption
that timerfd_timer_set_rate would not be called between enabling and
disabling continuous mode. What happened in this situation was that 
timerfd_timer_enable_continuous saved off our previously set timer (in this
situation a 0 timer, meaning it never runs out). Then timerfd_timer_disable_continuous
would restore this 0 timer, even though it logically should set the timer to be whatever
was set in timerfd_timer_set_rate.

Now the behavior in timerfd_timer_set_rate is to overwrite the saved timer that may
or may not have been set in timerfd_timer_enable_continuous. Even if
timerfd_timer_enable_continuous has not been previously called, this will not harm the
operation.

Thanks to Terry Wilson for discovering the problem and giving me a really great debug
capture that pointed out the problem clearly



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@168898 65c4cc65-6c06-0410-ace0-fbb531ad65f3

res/res_timing_timerfd.c

@@ -131,13 +131,21 @@ static void timerfd_timer_close(int handle)
 
 static int timerfd_timer_set_rate(int handle, unsigned int rate)
 {
-	struct itimerspec itspec;
-	itspec.it_value.tv_sec = 0;
-	itspec.it_value.tv_nsec = rate ? (long) (1000000000 / rate) : 0L;
-	itspec.it_interval.tv_sec = itspec.it_value.tv_sec;
-	itspec.it_interval.tv_nsec = itspec.it_value.tv_nsec;
+	struct timerfd_timer *our_timer, find_helper = {
+		.handle = handle,
+	};
+
+	if (!(our_timer = ao2_find(timerfd_timers, &find_helper, OBJ_POINTER))) {
+		ast_log(LOG_ERROR, "Couldn't find timer with handle %d\n", handle);
+		return -1;
+	}
+
+	our_timer->saved_timer.it_value.tv_sec = 0;
+	our_timer->saved_timer.it_value.tv_nsec = rate ? (long) (1000000000 / rate) : 0L;
+	our_timer->saved_timer.it_interval.tv_sec = our_timer->saved_timer.it_value.tv_sec;
+	our_timer->saved_timer.it_interval.tv_nsec = our_timer->saved_timer.it_value.tv_nsec;
 
-	return timerfd_settime(handle, 0, &itspec, NULL);
+	return timerfd_settime(handle, 0, &our_timer->saved_timer, NULL);
 }
 
 static void timerfd_timer_ack(int handle, unsigned int quantity)