netutils: iperf: Add pthread_join() to wait for completion

Summary:
- I noticed that lc823450-xgevk:rndis does not work with iperf
- Finally, I found that it does not call pthread_join()
- This commit fixes this issue

Impact:
- No impact

Testing:
- Tested with lc823450-xgevk:rndis
- NOTE: need to add iperf in the defconfig

Signed-off-by: Masayuki Ishikawa <Masayuki.Ishikawa@jp.sony.com>

netutils/iperf/iperf.c

@@ -653,6 +653,7 @@ static uint32_t iperf_get_buffer_len(void)
 int iperf_start(struct iperf_cfg_t *cfg)
 {
   int ret;
+  void *retval;
   struct sched_param param;
   pthread_t thread;
   pthread_attr_t attr;
@@ -696,6 +697,7 @@ int iperf_start(struct iperf_cfg_t *cfg)
       return -1;
     }
 
+  pthread_join(thread, &retval);
   return 0;
 }