Add `RDS_CMSG_RXPATH_LATENCY` to `socket`

Feature or enhancement

Proposal:

This issue suggests adding new RDS constants.

s = /* a RDS type socket */
msg, ancdata, flags, addr = s.recvmsg(2048, socket.CMSG_LEN(5 * 128))
for cmsg_level, cmsg_type, cmsg_data in ancdata:
    if cmsg_type == RDS_CMSG_RXPATH_LATENCY:
        # some processing

It‘s used to query the rx-path(that's receive) latency of RDS. Usually used to optimize RDS communication, such as controlling the number of connections and other strategies

Has this already been discussed elsewhere?

No response given

Links to previous discussion of this feature:

No response

Linked PRs

• gh-127384

首先检查 socket 模块对 RDS 辅助数据的处理，以及提案中描述的 recvmsg 路径。检查链接的 PR gh-127384，了解当前实现和预期的测试覆盖；完成意味着常量 RDS_CMSG_RXPATH_LATENCY 已公开，并且可以与所示的辅助数据流一起使用。