Can't set TCP receive buffer size

I am trying to send large files using `async-std` and have noticed that the default receiving buffer size seems to be significantly bottle-necking throughput (see [here](https://stackoverflow.com/questions/65731653/how-to-efficiently-send-large-files-across-a-single-network-connection?noredirect=1#comment116237731_65731653)). Is there a reason why there isn't an API method for this? [Tokio used to support this.](https://docs.rs/tokio/0.2.9/tokio/net/struct.TcpStream.html#method.set_recv_buffer_size)