stats: more accurate interval handling

In the stats loop sleep for a time period more closely matching
the stats.interval setting. Fix an off by one that would make
the loop wake up ~1 second early.

Bug #2716

src/counters.c

@@ -340,7 +340,6 @@ static void *StatsMgmtThread(void *arg)
 {
     ThreadVars *tv_local = (ThreadVars *)arg;
     uint8_t run = 1;
-    struct timespec cond_time;
 
     /* Set the thread name */
     if (SCSetThreadName(tv_local->name) < 0) {
@@ -381,8 +380,11 @@ static void *StatsMgmtThread(void *arg)
             TmThreadsUnsetFlag(tv_local, THV_PAUSED);
         }
 
-        cond_time.tv_sec = time(NULL) + stats_tts;
-        cond_time.tv_nsec = 0;
+        struct timeval cur_timev;
+        gettimeofday(&cur_timev, NULL);
+
+        struct timespec cond_time = FROM_TIMEVAL(cur_timev);
+        cond_time.tv_sec += (stats_tts);
 
         /* wait for the set time, or until we are woken up by
          * the shutdown procedure */

src/util-time.h

@@ -40,6 +40,9 @@ void TimeDeinit(void);
 void TimeSetByThread(const int thread_id, const struct timeval *tv);
 void TimeGet(struct timeval *);
 
+/** \brief intialize a 'struct timespec' from a 'struct timeval'. */
+#define FROM_TIMEVAL(timev) { .tv_sec = (timev).tv_sec, .tv_nsec = (timev).tv_usec * 1000 }
+
 #ifdef UNITTESTS
 void TimeSet(struct timeval *);
 void TimeSetToCurrentTime(void);