Fix a problem where CPU time was computed wrong.

This definitely affected FreeBSD, which breaks POSIX.1 by not
setting CLOCKS_PER_SEC to 1000000 (see clock(3)).  At this point
I can't tell if any other platforms were affected by this.

src/iperf_util.c

@@ -189,7 +189,7 @@ cpu_util(double pcpu[3])
     systemdiff = ((rtemp.ru_stime.tv_sec * 1000000.0 + rtemp.ru_stime.tv_usec) -
                   (rlast.ru_stime.tv_sec * 1000000.0 + rlast.ru_stime.tv_usec));
 
-    pcpu[0] = ((ctemp - clast) / timediff) * 100;
+    pcpu[0] = (((ctemp - clast) * 1000000.0 / CLOCKS_PER_SEC) / timediff) * 100;
     pcpu[1] = (userdiff / timediff) * 100;
     pcpu[2] = (systemdiff / timediff) * 100;
 }