clients: Change iterative-query-controller to use Link

Change-Id: I3b4fe73a467fb38c4fcde87481d1f84ec19c16c0
diff --git a/tests/unit/database-test-data.hpp b/tests/unit/database-test-data.hpp
index 104dd5d..26e092f 100644
--- a/tests/unit/database-test-data.hpp
+++ b/tests/unit/database-test-data.hpp
@@ -58,6 +58,7 @@
   Name m_certName;
   std::vector<Zone>  m_zones;
   std::vector<Rrset> m_rrsets;
+  std::vector<Link>  m_links;
 
   Zone m_root;
   Zone m_net;