*: 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/prng.c b/tests/prng.c
index 8d78ea5..bdcfb07 100644
--- a/tests/prng.c
+++ b/tests/prng.c
@@ -23,6 +23,8 @@
  * 02111-1307, USA.
  */
 
+#include <zebra.h>
+
 #include <assert.h>
 #include <stdlib.h>
 #include <string.h>