ipv4: avoid divide by zero in fib_rebalance

{
                    "product": "Linux",
                    "vendor": "Linux",
                    "defaultStatus": "unaffected",
                    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
                    "programFiles": [
                        "net/ipv4/fib_semantics.c"
                    ],
                    "versions": [
                        {
                            "version": "0e884c78ee19e902f300ed147083c28a0c6302f0",
                            "lessThan": "baf3a767b2845eb8e68f056ee4aa5b41b151e990",
                            "status": "affected",
                            "versionType": "git"
                        },
                        {
                            "version": "0e884c78ee19e902f300ed147083c28a0c6302f0",
                            "lessThan": "f655a26490e705ec76a79db7f412847fda342b39",
                            "status": "affected",
                            "versionType": "git"
                        },
                        {
                            "version": "0e884c78ee19e902f300ed147083c28a0c6302f0",
                            "lessThan": "7c68f4de5090b17b63b9a0a3b01b3807e01a296a",
                            "status": "affected",
                            "versionType": "git"
                        },
                        {
                            "version": "0e884c78ee19e902f300ed147083c28a0c6302f0",
                            "lessThan": "226a974054acbd892560bfa67f0ae8ffe271a736",
                            "status": "affected",
                            "versionType": "git"
                        },
                        {
                            "version": "0e884c78ee19e902f300ed147083c28a0c6302f0",
                            "lessThan": "0800c92ca5d1983df6843a5435299978901d1d02",
                            "status": "affected",
                            "versionType": "git"
                        },
                        {
                            "version": "0e884c78ee19e902f300ed147083c28a0c6302f0",
                            "lessThan": "5dac5c7ba8f5f3fb4bf29f2a2c3cb552f5b83c8f",
                            "status": "affected",
                            "versionType": "git"
                        },
                        {
                            "version": "0e884c78ee19e902f300ed147083c28a0c6302f0",
                            "lessThan": "d5520e815c4b1427104ce1428ee23821f2aa824d",
                            "status": "affected",
                            "versionType": "git"
                        },
                        {
                            "version": "0e884c78ee19e902f300ed147083c28a0c6302f0",
                            "lessThan": "5046d2880fec7d49ebed2fd2866747ee1d06ad71",
                            "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/ipv4/fib_semantics.c"
                    ],
                    "versions": [
                        {
                            "version": "4.4",
                            "status": "affected"
                        },
                        {
                            "version": "0",
                            "lessThan": "4.4",
                            "status": "unaffected",
                            "versionType": "semver"
                        },
                        {
                            "version": "5.10.273",
                            "lessThanOrEqual": "5.10.*",
                            "status": "unaffected",
                            "versionType": "semver"
                        },
                        {
                            "version": "5.15.224",
                            "lessThanOrEqual": "5.15.*",
                            "status": "unaffected",
                            "versionType": "semver"
                        },
                        {
                            "version": "6.1.191",
                            "lessThanOrEqual": "6.1.*",
                            "status": "unaffected",
                            "versionType": "semver"
                        },
                        {
                            "version": "6.6.161",
                            "lessThanOrEqual": "6.6.*",
                            "status": "unaffected",
                            "versionType": "semver"
                        },
                        {
                            "version": "6.12.115",
                            "lessThanOrEqual": "6.12.*",
                            "status": "unaffected",
                            "versionType": "semver"
                        },
                        {
                            "version": "6.18.59",
                            "lessThanOrEqual": "6.18.*",
                            "status": "unaffected",
                            "versionType": "semver"
                        },
                        {
                            "version": "7.2.13",
                            "lessThanOrEqual": "7.2.*",
                            "status": "unaffected",
                            "versionType": "semver"
                        },
                        {
                            "version": "7.3",
                            "lessThanOrEqual": "*",
                            "status": "unaffected",
                            "versionType": "original_commit_for_fix"
                        }
                    ]
                }