net: fix UaF in netns ops registration error path
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 v5.4.231 by commit ddd49cbbd4c1ceb38032018b589b44208e54f55e, it was introduced in version v5.4.223 by commit 97ad240fd9aa9214497d14af2b91608e20856cac. For more details please see the references link.