[Feature Request] Get new sites from peer exchange method.

I found in the code that the pex method is only used to increase the number of peers of serving site.
While it is also possible to find new sites which is not serving in my own peer but serving in all connected peers.
（Maybe I am wrong in reading the source code and this function has been released）

Start by locating the pex method and trace how it discovers serving sites and increases the serving site's peer count. Determine whether connected peers' non-serving sites can be discovered through this path; done means the requested new-site discovery behavior is implemented and verified without breaking existing peer exchange.

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