tests: fix missing array_size() include

 * tests/test-sig.c: add #include "lib/memory.h" to get array_size()

Signed-off-by: David Lamparter <equinox@opensourcerouting.org>
diff --git a/tests/test-sig.c b/tests/test-sig.c
index fe428de..df023fa 100644
--- a/tests/test-sig.c
+++ b/tests/test-sig.c
@@ -1,6 +1,7 @@
 #include <zebra.h>
 #include <sigevent.h>
 #include "lib/log.h"
+#include "lib/memory.h"
 
 void
 sighup (void)