[ONOS-4520] Separate ProtoBuf model from gRPC services

Change-Id: Ib1e1358b1fd49206cfd15ffbba3b1448376d1702
diff --git a/incubator/pom.xml b/incubator/pom.xml
index 2fd2b64..0ad62ed 100644
--- a/incubator/pom.xml
+++ b/incubator/pom.xml
@@ -36,6 +36,7 @@
         <module>core</module>
         <module>net</module>
         <module>store</module>
+        <module>protobuf</module>
         <module>rpc</module>
         <module>rpc-grpc</module>
     </modules>