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_server.cc b/aos/network/message_bridge_server.cc
index fa5e7c1..ee276d6 100644
--- a/aos/network/message_bridge_server.cc
+++ b/aos/network/message_bridge_server.cc
@@ -4,7 +4,7 @@
 #include "gflags/gflags.h"
 #include "glog/logging.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 {