Point message_bridge_{client,server} to config.json

Otherwise we need an argument on the robot for everything to run and
that is pretty annoying to work with.

Change-Id: Ibb04affb254c67fcb83c28a23fcaae97ea86b348
diff --git a/aos/network/message_bridge_client.cc b/aos/network/message_bridge_client.cc
index c44eee0..891a8a1 100644
--- a/aos/network/message_bridge_client.cc
+++ b/aos/network/message_bridge_client.cc
@@ -3,7 +3,7 @@
 #include "aos/events/shm_event_loop.h"
 #include "aos/init.h"
 
-DEFINE_string(config, "multinode_pingpong_config.json", "Path to the config.");
+DEFINE_string(config, "config.json", "Path to the config.");
 
 namespace aos {
 namespace message_bridge {