Add exclusion configuration for Javadoc.
Add exclusion configuration for Javadoc.

- Exclude ProtoBuf generated classes

Change-Id: I96211d2a6b49fb75286ffa1a7a7d3a96fa9e2817

opennetworkinglab/spring-open,opennetworkinglab/spring-open,opennetworkinglab/spring-open,opennetworkinglab/spring-open,opennetworkinglab/spring-open,opennetworkinglab/spring-open