Fix mistake in add_ns utility function

packet-exchange/src/utilities.c

@@ -9,7 +9,7 @@
 void add_ns(struct timespec *t, uint64_t ns) {
   t->tv_nsec += ns;
 
-  if ((unsigned int)t->tv_nsec >= NSEC_PER_SEC) {
+  while ((unsigned int)t->tv_nsec >= NSEC_PER_SEC) {
     t->tv_sec += 1;
     t->tv_nsec -= NSEC_PER_SEC;
   }