Fix instant vs overall rate in websocket C test

The overall rate was incorrect when using non-default intervals. Also
simplify the code using plain nanosecond values, and fix the rate for
the last event which was based on the number of sleeps instead of the
actual time elapsed.

tests/websocket.c

@@ -474,6 +474,8 @@ progress_thread_main(void *ptr) {
 
 	struct timespec ts_start;
 	clock_gettime(CLOCK_MONOTONIC, &ts_start);
+	long start_nanos = ts_start.tv_sec * 1e9 + ts_start.tv_nsec; /* time of monitoring start */
+	long last_print_nanos = start_nanos;
 
 	while(1) {
 		int sem_received = 0;
@@ -501,7 +503,6 @@ progress_thread_main(void *ptr) {
 		sem_received = 1;
 	}
 #endif
-		// nanosleep(&ts, NULL);
 		num_sleeps++;
 		int total_sent = 0, total_received = 0, any_broken = 0, num_complete = 0;
 		for (int i = 0; i < pt->worker_count; i++) {
@@ -515,11 +516,15 @@ progress_thread_main(void *ptr) {
 		}
 		struct timespec ts_after_sleep;
 		clock_gettime(CLOCK_MONOTONIC, &ts_after_sleep);
+		long after_sleep_nanos = ts_after_sleep.tv_sec * 1e9 + ts_after_sleep.tv_nsec;
+		long total_nanos = after_sleep_nanos - start_nanos; /* total time spent so far */
+
 		fprintf(stderr, "After %0.2f sec: %'d messages sent, %'d received (%.02f%%). Instant rate: %'ld/sec, overall rate: %'ld/sec\n",
 			((float)((ts_after_sleep.tv_sec * 1e9 + ts_after_sleep.tv_nsec) - (ts_start.tv_sec * 1e9 + ts_start.tv_nsec))) / (float)1e9,
 			total_sent, total_received, 100.0f * (float)total_received / (float)(pt->worker_count * pt->msg_target),
-			lroundf((float)(total_received - last_received) / pt->interval_sec),
+			lroundf((float)(total_received - last_received) / (((float)(after_sleep_nanos - last_print_nanos)) / 1e9f)),
-			lroundf((float)total_received / ((float)num_sleeps) * pt->interval_sec));
+			lroundf((float)total_received / (((float)total_nanos) / 1e9f)));
+		last_print_nanos = after_sleep_nanos; /* time of last print */
 
 		if (sem_received || total_received == pt->msg_target * pt->worker_count || any_broken || num_complete == pt->worker_count) {
 			break;