msg/async/rdma: use ibv_port_attr object type in Port class

msg/async/rdma: use ibv_port_attr object type in Port class

1. Avoid to do memory management without using pointer to operate
operate the allocated space. Or, it could have memory leak.
2. Since member type has been changed in class Device, it need
to use member domain operator "." to access to the sub-member in
object.
3. There's no need to consider experimental API of ibv_query_port.
So, merge ibv_query_port in the prolog.

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