fix bug: switch between stream_rpc and baidu_std

[howarlii]

What problem does this PR solve?

Issue Number: https://github.com/apache/brpc/issues/2677

Problem Summary: under baidu_std, server can not parse message when normal PRC and stream RPC arrive simultaneously

What is changed and the side effects?

Changed: switch between baidu_std and stream_rpc in InputMessenger::CutInputMessage

Side effects:

• Performance effects(性能影响): Little or none

• Breaking backward compatibility(向后兼容性): no

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Check List:

• Please make sure your changes are compilable(请确保你的更改可以通过编译).
• When providing us with a new feature, it is best to add related tests(如果你向我们增加一个新的功能, 请添加相关测试).
• Please follow Contributor Covenant Code of Conduct.(请遵循贡献者准则).

[wwbmmm]

UT failed：

brpc_streaming_rpc_unittest.cpp:254: Failure
Expected equality of these values:
  0
  brpc::StreamWrite(request_stream, out)
    Which is: 11

[howarlii]

这个似乎是UT的概率fail问题，main上的UT也是fail的

[wwbmmm]

LGTM