openflow_input: fix role_request/reply

Lists the role as enum ofp_controller role
Changes the body of the reply to match the body of the request as per spec
java_gen: add OFGroup
openflow_input: make stats_request/reply flags use enum
Merge into master from pull request #97:
A few fixes in openflow_input for enums, and add support for type OFGroup in java_gen (https://github.com/floodlight/loxigen/pull/97)