*: make sure zebra.h is always included first

zebra.h pulls in config.h, which results in fiddling with things like
__FILE_OFFSET_BITS. It must always be included first, in order to set
flags that influence the compiler via <features.h>.

Signed-off-by: David Lamparter <equinox@opensourcerouting.org>
diff --git a/tests/test-timer-correctness.c b/tests/test-timer-correctness.c
index 47c0b73..e523929 100644
--- a/tests/test-timer-correctness.c
+++ b/tests/test-timer-correctness.c
@@ -23,11 +23,11 @@
  * 02111-1307, USA.
  */
 
+#include <zebra.h>
+
 #include <stdio.h>
 #include <unistd.h>
 
-#include <zebra.h>
-
 #include "memory.h"
 #include "pqueue.h"
 #include "prng.h"