redis: Use the ff_gettimeofday instead of gettimeofday.

In the redis, the gettimeofday uses too much CPU, even using the
vdso. This patch is useful to avoid wasting CPU cycles and
improve the performance.

Signed-off-by: Tonghao Zhang <xiangxia.m.yue@gmail.com>

app/redis-3.2.8/src/ae.c

@@ -185,7 +185,12 @@ static void aeGetTime(long *seconds, long *milliseconds)
 {
     struct timeval tv;
 
+#ifdef HAVE_FF_KQUEUE
+    ff_gettimeofday(&tv, NULL);
+#else
     gettimeofday(&tv, NULL);
+#endif
+
     *seconds = tv.tv_sec;
     *milliseconds = tv.tv_usec/1000;
 }