patch by Chrysn: patch #8704 fix sys_timeouts_sleeptime function

CHANGELOG

@@ -249,6 +249,9 @@ HISTORY
 
   ++ Bugfixes:
 
+  2015-08-18: Chrysn
+  timers.c: patch #8704 fix sys_timeouts_sleeptime function
+
   2015-07-01: Erik Ekman
   * puf.c: fixed bug #45454 (pbuf_take_at() skips write and returns OK if offset
     is at start of pbuf in chain)

src/core/timers.c

@@ -495,10 +495,16 @@ sys_restart_timeouts(void)
 u32_t
 sys_timeouts_sleeptime(void)
 {
+  u32_t diff;
   if (next_timeout == NULL) {
     return 0xffffffff;
   }
-  return (sys_now() - timeouts_last_time) + next_timeout->time;
+  diff = sys_now() - timeouts_last_time;
+  if (diff > next_timeout->time) {
+    return 0;
+  } else {
+    return next_timeout->time - diff;
+  }
 }
 
 #else /* NO_SYS */