java_gen: small improvements to gen_table/tlv extensions

 - move bsntlv classes to dedicated package/factory
 - change type of of_bsn_tlv_vlan_vid to VlanVid
 - change type of tableId to new typesafe constant GenTableId
diff --git a/test_data/of13/bsn_gentable_desc_stats_reply.data b/test_data/of13/bsn_gentable_desc_stats_reply.data
index 64346c8..180a8a1 100644
--- a/test_data/of13/bsn_gentable_desc_stats_reply.data
+++ b/test_data/of13/bsn_gentable_desc_stats_reply.data
@@ -43,13 +43,13 @@
     .setEntries(
         ImmutableList.<OFBsnGentableDescStatsEntry>of(
             factory.buildBsnGentableDescStatsEntry()
-                .setTableId(0)
+                .setTableId(GenTableId.of(0))
                 .setName("table 0")
                 .setBucketsSize(32)
                 .setMaxEntries(64)
                 .build(),
             factory.buildBsnGentableDescStatsEntry()
-                .setTableId(1)
+                .setTableId(GenTableId.of(1))
                 .setName("table 1.........................")
                 .setBucketsSize(64)
                 .setMaxEntries(128)