ngx_stream_pass_module: add an option to allow keeping the incoming stream server_port

Describe the feature you'd like to add to nginx

With ngx_stream_pass_module, one can pass a connection directly from stream to a http server. For now, the passed connection into http context will see the http server_port instead of the real incoming stream server_port.

When a HTTP request can come from both the http server and stream server, one may want see the incoming stream server_port, so one can tell where the request is coming from.

Describe the problem this feature solves

For now there is no such option. Connections' local_addr is forced to set to the http server listening address.

Additional context

A simple boolean option can be added to pass directive.