ipv6: mcast: use rcu_assign_pointer() for __rcu list updates

{
                    "product": "Linux",
                    "vendor": "Linux",
                    "defaultStatus": "unaffected",
                    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
                    "programFiles": [
                        "net/ipv6/mcast.c"
                    ],
                    "versions": [
                        {
                            "version": "456b61bca8ee324ab6c18b065e632c9a8c88aa39",
                            "lessThan": "0e3e3cec28c4d1bf29948da40b4e9e5d44f7852b",
                            "status": "affected",
                            "versionType": "git"
                        },
                        {
                            "version": "456b61bca8ee324ab6c18b065e632c9a8c88aa39",
                            "lessThan": "49d7e1b456ba2f3ee08b3e264d999c09992cde8e",
                            "status": "affected",
                            "versionType": "git"
                        },
                        {
                            "version": "456b61bca8ee324ab6c18b065e632c9a8c88aa39",
                            "lessThan": "afca229b39acc2590976b3e4f6e0fe76cededc60",
                            "status": "affected",
                            "versionType": "git"
                        },
                        {
                            "version": "456b61bca8ee324ab6c18b065e632c9a8c88aa39",
                            "lessThan": "2e46b0c9fcf7e10b64ce1630b925f47918d1f7f6",
                            "status": "affected",
                            "versionType": "git"
                        },
                        {
                            "version": "456b61bca8ee324ab6c18b065e632c9a8c88aa39",
                            "lessThan": "0c8f56c583c3250408367880c98e4d6fbc929315",
                            "status": "affected",
                            "versionType": "git"
                        }
                    ]
                }

{
                    "product": "Linux",
                    "vendor": "Linux",
                    "defaultStatus": "affected",
                    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
                    "programFiles": [
                        "net/ipv6/mcast.c"
                    ],
                    "versions": [
                        {
                            "version": "2.6.38",
                            "status": "affected"
                        },
                        {
                            "version": "0",
                            "lessThan": "2.6.38",
                            "status": "unaffected",
                            "versionType": "semver"
                        },
                        {
                            "version": "6.6.160",
                            "lessThanOrEqual": "6.6.*",
                            "status": "unaffected",
                            "versionType": "semver"
                        },
                        {
                            "version": "6.12.114",
                            "lessThanOrEqual": "6.12.*",
                            "status": "unaffected",
                            "versionType": "semver"
                        },
                        {
                            "version": "6.18.57",
                            "lessThanOrEqual": "6.18.*",
                            "status": "unaffected",
                            "versionType": "semver"
                        },
                        {
                            "version": "7.2.7",
                            "lessThanOrEqual": "7.2.*",
                            "status": "unaffected",
                            "versionType": "semver"
                        },
                        {
                            "version": "7.3",
                            "lessThanOrEqual": "*",
                            "status": "unaffected",
                            "versionType": "original_commit_for_fix"
                        }
                    ]
                }