build: check for linux/genetlink.h

Change-Id: Id18fcc81a49e769a05c4416cdce03022a2179051
Refs: #4020
diff --git a/src/net/detail/netlink-socket.hpp b/src/net/detail/netlink-socket.hpp
index 4a6e4f1..080d169 100644
--- a/src/net/detail/netlink-socket.hpp
+++ b/src/net/detail/netlink-socket.hpp
@@ -31,7 +31,7 @@
 #include <map>
 #include <vector>
 
-#ifndef NDN_CXX_HAVE_RTNETLINK
+#ifndef NDN_CXX_HAVE_NETLINK
 #error "This file should not be included ..."
 #endif