openflow_input: make of_flow_stats_entry.flags use enum type

The flow stats entry was still using uint16, while the flod_add etc.
messages were using enum ofp_flow_mod_flags.
java_gen: U128: add unit test for readBytes
java_gen: make of_bsn_table_set_buckets_size use table_id type
java_gen/pom.xml: Bounce artifact version to 0.3.7-SNAPSHOT

For the API change in 078fcfd97
Merge into master from pull request #289:
Fix type of of_flow_stats_entry.flags, smaller fixes to Java (https://github.com/floodlight/loxigen/pull/289)