vhost_user_net: Move binary into vhost_user_net crate

The binary is still built in the same location but the source code and
the dependencies for it come from the vhost_user_net crate itself.

The binary will be built with:

`cargo build --all --bin vhost_user_net` or just `cargo build --all`

Signed-off-by: Rob Bradford <robert.bradford@intel.com>

src/bin/vhost_user_net.rs

@@ -1,32 +0,0 @@
-// Copyright 2019 Intel Corporation. All Rights Reserved.
-//
-// Portions Copyright 2018 Amazon.com, Inc. or its affiliates. All Rights Reserved.
-//
-// Portions Copyright 2017 The Chromium OS Authors. All rights reserved.
-//
-// SPDX-License-Identifier: (Apache-2.0 AND BSD-3-Clause)
-
-#[macro_use(crate_version, crate_authors)]
-extern crate clap;
-extern crate vhost_user_net;
-
-use clap::{App, Arg};
-use vhost_user_net::start_net_backend;
-
-fn main() {
-    let cmd_arguments = App::new("vhost-user-net backend")
-        .version(crate_version!())
-        .author(crate_authors!())
-        .about("Launch a vhost-user-net backend.")
-        .arg(
-            Arg::with_name("net-backend")
-                .long("net-backend")
-                .help(vhost_user_net::SYNTAX)
-                .takes_value(true)
-                .min_values(1),
-        )
-        .get_matches();
-
-    let backend_command = cmd_arguments.value_of("net-backend").unwrap();
-    start_net_backend(backend_command);
-}