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_clear_request.data b/test_data/of13/bsn_gentable_clear_request.data
index 911ee27..847af3c 100644
--- a/test_data/of13/bsn_gentable_clear_request.data
+++ b/test_data/of13/bsn_gentable_clear_request.data
@@ -18,7 +18,7 @@
 builder.setXid(0x12345678)
     .setChecksum(OFChecksum128.of(0xFEDCBA9876543210L, 0xFFEECCBBAA990000L))
     .setChecksumMask(OFChecksum128.of(0xFFFFFFFFFFFFFFFFL, 0xFFFFFFFFFFFF0000L))
-    .setTableId(20)
+    .setTableId(GenTableId.of(20))
 -- c
 obj = of_bsn_gentable_clear_request_new(OF_VERSION_1_3);
 of_bsn_gentable_clear_request_xid_set(obj, 0x12345678);