CVE-2026-99071: ipv4: do not warn on route notification size race

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

ipv4: do not warn on route notification size race

Commit 680aea08e78c ("net: ipv4: Emit notification when fib hardware flags are changed") added asynchronous route notifications for hardware flag changes.

fibaliashwflagsset() sizes the skb with fibnlmsgsize() and later fills it with fibdumpinfo() while holding only RCU. With nexthop compatibility mode enabled, a concurrent replacement can grow the group between these independent snapshots. fibdumpinfo() can then legitimately return -EMSGSIZE, so the warning does not prove a sizing bug.

Remove the warning. The existing error path still frees the skb and reports the error to listeners.