Add TORCH_API to expose RPC module functions for RPC module device extension (#108553)
At present, I refer to the existing rpc backend tensorpipe backend, and implement our own rpc communication backend in our extension package. We found that these functions are not exposed during development, and direct use will cause our extension package to appear undefined symbol problem.
Add the TORCH_API macro to the functions required to implement the custom tensorpipe agent in the rpc module to expose them to developers，at the same time, we think this risk is very controllable and hope it can be merged into the version 2.1.
cc
@albanD, @kumpera
Pull Request resolved: https://github.com/pytorch/pytorch/pull/108553
Approved by: https://github.com/kumpera, https://github.com/albanD
