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 v4.19.272 by commit ad0dfe9bcf0d78e699c7efb64c90ed062dc48bea, it was introduced in version v4.19.264 by commit 5a2ea549be94924364f6911227d99be86e8cf34a. For more details please see the references link.