AZL-111221: CVE-2026-99121 affecting package kernel 6.6.157.1-1

In the Linux kernel, the following vulnerability has been resolved:

ipv4: avoid divide by zero in fibrebalance

fibrebalance() computes the total eligible nexthop weight in one pass and programs upper bounds in a second pass. A concurrent change to ignorerouteswithlinkdown can make the first pass return zero while the second pass sees an eligible nexthop, resulting in division by zero.

If the first pass reports a zero total, set each nexthop upper bound to -1 and skip the division. This matches the IPv6 fix in commit d2c26c2911dd ("ipv6: avoid divide by zero in rt6multipathrebalance") and preserves the lock-free rebalance path.