Add missing namespace for binder transport phony implementation (#27225)

Also order the definitions correctly

src/core/ext/transport/binder/client/channel_create.cc

@@ -105,18 +105,24 @@ std::shared_ptr<grpc::Channel> CreateBinderChannel(
 
 #else  // !GPR_SUPPORT_BINDER_TRANSPORT
 
-std::shared_ptr<grpc::Channel> CreateBinderChannel(void*, jobject,
-                                                   absl::string_view,
+namespace grpc {
+namespace experimental {
+
+void BindToOnDeviceServerService(void*, jobject, absl::string_view,
                                  absl::string_view) {
   GPR_ASSERT(0);
-  return {};
 }
 
-void BindToOnDeviceServerService(void*, jobject, absl::string_view,
+std::shared_ptr<grpc::Channel> CreateBinderChannel(void*, jobject,
+                                                   absl::string_view,
                                                    absl::string_view) {
   GPR_ASSERT(0);
+  return {};
 }
 
+}  // namespace experimental
+}  // namespace grpc
+
 #endif  // GPR_SUPPORT_BINDER_TRANSPORT
 
 #endif  // GPR_ANDROID