CVE-2026-19742 IPv6 stable and temporary interface identifiers derived from a non-cryptographic PRNG secret key

The IPv6 stack derived the long-lived secret key used to compute RFC 7217 stable interface identifiers genstableiid in subsys/net/ip/ipv6.c and RFC 8981 temporary interface identifiers gentemporaryiid in subsys/net/ip/ipv6pe.c with sysrandget. That API is documented as not cryptographically secur...