Exclude gRPC generated code from javadoc processing

- part of ONOS-3323

Change-Id: Ie5975ace5e8ade2032eba726c59da2736502295b
diff --git a/docs/internal-excludes b/docs/internal-excludes
index 9876cce..2ae8a26 100644
--- a/docs/internal-excludes
+++ b/docs/internal-excludes
@@ -3,3 +3,5 @@
 org.onlab.thirdparty
 org.onosproject.oecfg
 org.onosproject.maven
+org.onosproject.grpc*
+protobuf.*