ipv6: avoid divide by zero in rt6_multipath_rebalance

{
                    "product": "Linux",
                    "vendor": "Linux",
                    "defaultStatus": "unaffected",
                    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
                    "programFiles": [
                        "net/ipv6/route.c"
                    ],
                    "versions": [
                        {
                            "version": "bd11ff421d36abdb585b9104fa70057bf01b3110",
                            "lessThan": "f30cf8fd9872299c0c27f9916252ba2b9f422dce",
                            "status": "affected",
                            "versionType": "git"
                        },
                        {
                            "version": "bd11ff421d36abdb585b9104fa70057bf01b3110",
                            "lessThan": "f82b5dbb2fef65b52a62d5ffe05e0483c4385a83",
                            "status": "affected",
                            "versionType": "git"
                        },
                        {
                            "version": "bd11ff421d36abdb585b9104fa70057bf01b3110",
                            "lessThan": "d2c26c2911dd1a363c488add4fb63eb5f0f28f87",
                            "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/route.c"
                    ],
                    "versions": [
                        {
                            "version": "6.16",
                            "status": "affected"
                        },
                        {
                            "version": "0",
                            "lessThan": "6.16",
                            "status": "unaffected",
                            "versionType": "semver"
                        },
                        {
                            "version": "6.18.52",
                            "lessThanOrEqual": "6.18.*",
                            "status": "unaffected",
                            "versionType": "semver"
                        },
                        {
                            "version": "7.2.6",
                            "lessThanOrEqual": "7.2.*",
                            "status": "unaffected",
                            "versionType": "semver"
                        },
                        {
                            "version": "7.3",
                            "lessThanOrEqual": "*",
                            "status": "unaffected",
                            "versionType": "original_commit_for_fix"
                        }
                    ]
                }