rtnetlink_server: Avoid refreshing for gateway changes

Instead of refreshing all of the objects, we can just update the
ethernet object that has the gateway route.

Change-Id: Ib1922273b625b1400625c6a851330e3642a8c647
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/src/network_manager_main.cpp b/src/network_manager_main.cpp
index 80276b3..1c2e38e 100644
--- a/src/network_manager_main.cpp
+++ b/src/network_manager_main.cpp
@@ -292,7 +292,7 @@
     manager = std::make_unique<Manager>(bus, DEFAULT_OBJPATH, NETWORK_CONF_DIR);
 
     // RTNETLINK event handler
-    netlink::Server svr(event);
+    netlink::Server svr(event, *manager);
 
 #ifdef SYNC_MAC_FROM_INVENTORY
     std::ifstream in(configFile);