rest_qos: fix error of additional a qos rule with "priority"

Currently, rest_qos is impossible to set the "priority" of when to set the QoS rule to switch.
This patch fixes this problem.

Also, "priority" is should be the same column as "match" and "actions".
As a result, now rest_qos possible to set the "priority" in the following curl command.

e.g.)
  $ curl -X POST -d '{"priority":"5",
                      "match": {"nw_dst": "10.0.0.1", "nw_proto": "UDP", "tp_dst": "5002"},
                      "actions":{"queue": "1"}}' http://localhost:8080/qos/rules/0000000000000001

Reported-by: Jace Liang <b436412@gmail.com>
Signed-off-by: Minoru TAKAHASHI <takahashi.minoru7@gmail.com>