misc: net_util: drop extern crate, use modern rust

This commit is part of a series of similar commits.

Signed-off-by: Philipp Schuster <philipp.schuster@cyberus-technology.de>
On-behalf-of: SAP philipp.schuster@sap.com

net_util/src/open_tap.rs

@@ -6,6 +6,7 @@ use std::net::IpAddr;
 use std::path::Path;
 use std::{fs, io};
 
+use log::warn;
 use thiserror::Error;
 
 use super::{MacAddr, Tap, TapError, vnet_hdr_len};