*: use array_size() helper macro

Use the array_size() helper macro.  Replaces several instances of local
macros with the same definition.

Reviewed-by: Scott Feldman <sfeldma@cumulusnetworks.com>
Signed-off-by: David Lamparter <equinox@opensourcerouting.org>
diff --git a/zebra/zebra_rib.c b/zebra/zebra_rib.c
index b8a4703..0e29e61 100644
--- a/zebra/zebra_rib.c
+++ b/zebra/zebra_rib.c
@@ -1546,7 +1546,7 @@
   /* Set default distance by route type. */
   if (distance == 0)
     {
-      if ((unsigned)type >= sizeof(route_info) / sizeof(route_info[0]))
+      if ((unsigned)type >= array_size(route_info))
 	distance = 150;
       else
         distance = route_info[type].distance;