net: fix a resource leak in copy_net_ns() error handling path

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                    "defaultStatus": "unaffected",
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                        "net/core/net_namespace.c"
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{
                    "product": "Linux",
                    "vendor": "Linux",
                    "defaultStatus": "affected",
                    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
                    "programFiles": [
                        "net/core/net_namespace.c"
                    ],
                    "versions": [
                        {
                            "version": "6.18",
                            "status": "affected"
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