ethtool: do not perform operations on net devices being unregistered

ethtool: do not perform operations on net devices being unregistered

This is an automated ID intended to aid in discovery of potential security vulnerabilities. The actual impact and attack plausibility have not yet been proven.
This ID is fixed in Linux Kernel version v5.15.8 by commit cfd719f04267108f5f5bf802b9d7de69e99a99f9, it was introduced in version v5.6 by commit 041b1c5d4a53e97fc9e029ae32469552ca12cb9b. For more details please see the references link.