Fix test-cache-mngr test

Needs to include <netlink-private/cache-api.h>

Reported-by: Jeroen Roovers <jer@gentoo.org>
Signed-off-by: Thomas Graf <tgraf@suug.ch>
diff --git a/tests/test-cache-mngr.c b/tests/test-cache-mngr.c
index da17018..8999e58 100644
--- a/tests/test-cache-mngr.c
+++ b/tests/test-cache-mngr.c
@@ -3,6 +3,8 @@
 #include <netlink/cli/utils.h>
 #include <signal.h>
 
+#include <netlink-private/cache-api.h>
+
 static int quit = 0;
 
 static struct nl_dump_params dp = {