CVE-2026-74290: net/sched: cls_flow: Dont expose folded kernel pointers

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

net/sched: clsflow: Dont expose folded kernel pointers

The flow classifier falls back to addrfold() for fields that are missing from packet headers. In map mode, userspace controls mask, xor, rshift, addend and divisor, and can observe the resulting classid through class statistics. This allows a tc classifier in a user/network namespace to recover the 32-bit folded value of skb->sk, skbdst() or skbnfct().

Align with standard kernel practices for pointer hashing and replace the XOR folding with a keyed siphash (which is cryptographically secure)