ofctl_v1_3: Fix to enable using meter flags multiply

ofctl_rest is now enabled to parse flags multiply as follows:

  curl -X POST -d '{"dpid": 1,
                    "meter_id": 1,
                    "flags": ["KBPS", "BURST"],
                    "bands": [{"type": "DROP", "rate": 1000}]}' http://localhost:8080/stats/meterentry/add

And now enabled to show flags as follows:

  curl http://localhost:8080/stats/meterconfig/1

  {
    "1": [
      {"bands": [{"burst_size": 0, "rate": 1000, "type": "DROP"}],
       "flags": ["KBPS", "BURST"], "meter_id": 1}
    ]
  }

Reported-by: cheers <cnmjbm@gmail.com>
Signed-off-by: Yuichi Ito <ito.yuichi0@gmail.com>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>