msg/async/rdma: fix error argument to get right qp state

msg/async/rdma: fix error argument to get right qp state

1. It's wrong to use "-1" as argument to query queue state.
In rdma library, ibv_query_qp will call ibv_cmd_query_qp to query
queue state. If "-1" is used as attr_mask, ibv_cmd_query_qp will
return error EOPNOTSUPP which means query failed.

2. In class QueuePair, is_error() could use member function get_state()
to get the queue pair state.

3. It's better to use qp_state as queue pair state according to
ibv_query_qp manual guide.
   struct ibv_qp_attr {
      enum ibv_qp_state       qp_state;            /* Current QP state */
      enum ibv_qp_state       cur_qp_state;        /* Current QP state - irrelevant for ibv_query_qp */
      ...

Signed-off-by: Changcheng Liu <changcheng.liu@aliyun.com>