Adding build tools for gRPC compilation.
ONOS-6095

Change-Id: I80687eb2a91ad60c4dbec0bb966e917555d46151
diff --git a/modules.defs b/modules.defs
index 9d0b53e..13cd632 100644
--- a/modules.defs
+++ b/modules.defs
@@ -9,6 +9,7 @@
 API = [
     '//core/api:onos-api',
     '//incubator/api:onos-incubator-api',
+    '//incubator/protobuf:onos-incubator-grpc',
 ]
 
 CORE = UTILS + API + [