net_util: Move virtio-net helpers to net_util crate

Moving helpers to the net_util crate since we don't want virtio-net
common code to be split between two places. The net_util crate should be
the only place to host virtio-net common code.

Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>

virtio-devices/src/vhost_user/net.rs

@@ -1,14 +1,13 @@
 // Copyright 2019 Intel Corporation. All Rights Reserved.
 // SPDX-License-Identifier: Apache-2.0
 
-use super::super::net_util::{build_net_config_space, VirtioNetConfig};
 use super::super::{
     ActivateError, ActivateResult, Queue, VirtioCommon, VirtioDevice, VirtioDeviceType,
 };
 use super::vu_common_ctrl::*;
 use super::{Error, Result};
 use crate::VirtioInterrupt;
-use net_util::MacAddr;
+use net_util::{build_net_config_space, MacAddr, VirtioNetConfig};
 use std::ops::Deref;
 use std::os::unix::io::AsRawFd;
 use std::os::unix::net::UnixListener;