Avoid aggregate initialization for tensorpipe::{Cpu,Cuda}Buffer and tensorpipe::Message::Tensor. (#55136)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/55136
This will ease the transition to the new API where `Buffer` does not
store a length anymore.
Test Plan: CI
Reviewed By: lw
Differential Revision: D27466385
fbshipit-source-id: 9a167f8c501455a3ab49ce75257c69d8b4869925
