Table 20 and 21 entries not installed in single dpn scenario

When vpn service is configured for single dpn 2 hosts scenario, the table 20 and 21 entries are not being configured in the switch.

Steps:
====
->install vpnservice
>connect switch h1-s1--h2
->Create vpn instance
->Create ietf interfaces for s1-eth1 and s1-eth2
->create vpn insterfaces for s1-eth1 and s1-eth2

Fib entries are seen in the datastore for the 2 hosts as below:

Fib entries:
===========
http://localhost:8181/restconf/config/odl-fib:fibEntries/
Response Body
{
"fibEntries": {
"vrfTables": [
{
"routeDistinguisher": "4000:1",
"vrfEntry": [

{ "destPrefix": "10.0.0.2", "label": 2 }

,

{ "destPrefix": "10.0.0.1", "label": 3 }

]
}
]
}
}

Switch entries:
===========
mininet> dpctl dump-groups -O OpenFlow13

• • • s1 ------------------------------------------------------------------------
      OFPST_GROUP_DESC reply (OF1.3) (xid=0x2):
      group_id=1,type=indirect,bucket=weight:0,actions=pop_mpls:0x0800,set_field:d2:18:94:2b:ce:29->eth_dst,output:2
      group_id=2,type=indirect,bucket=weight:0,actions=pop_mpls:0x0800,set_field:aa:18:58:dd:12:55->eth_dst,output:1
      mininet> dpctl dump-flows -O OpenFlow13
    • s1 ------------------------------------------------------------------------
      OFPST_FLOW reply (OF1.3) (xid=0x2):
      cookie=0x8000001, duration=1011.452s, table=0, n_packets=0, n_bytes=0, priority=10,in_port=1 actions=write_metadata:0x1/0xffffffff,goto_table:21
      cookie=0x8000001, duration=1011.465s, table=0, n_packets=0, n_bytes=0, priority=10,in_port=2 actions=write_metadata:0x1/0xffffffff,goto_table:21
      cookie=0x1030000, duration=1343.440s, table=20, n_packets=0, n_bytes=0, priority=0 actions=write_actions(CONTROLLER:65535)
      cookie=0x8000003, duration=1343.440s, table=21, n_packets=0, n_bytes=0, priority=0 actions=write_actions(CONTROLLER:65535)
      mininet>

Errors observed in the controller:
=========================

2015-05-18 15:45:24,497 | ERROR | lt-dispatcher-30 | FibManager | 215 - org.opendaylight.vpnservice.fibmanager-impl - 0.1.0.SNAPSHOT | Could not get nexthop group id for nexthop: null in vpn 4000:1
2015-05-18 15:45:24,497 | WARN | lt-dispatcher-30 | FibManager | 215 - org.opendaylight.vpnservice.fibmanager-impl - 0.1.0.SNAPSHOT | Failed to add Route: 10.0.0.2 in vpn: 4000:1
2015-05-18 15:45:24,498 | ERROR | lt-dispatcher-30 | FibManager | 215 - org.opendaylight.vpnservice.fibmanager-impl - 0.1.0.SNAPSHOT | Could not get nexthop group id for nexthop: null in vpn 4000:1
2015-05-18 15:45:24,499 | WARN | lt-dispatcher-30 | FibManager | 215 - org.opendaylight.vpnservice.fibmanager-impl - 0.1.0.SNAPSHOT | Failed to add Route: 10.0.0.1 in vpn: 4000:1

Workaround:
==========
Workaroung is to configure GRE tunnel for single dpn scenario also.