CVE-2026-79980 Predictable and reused DHCPv4 transaction identifier allows spoofed DHCP replies to reconfigure gateway and DNS

The DHCPv4 client in subsys/net/lib/dhcpv4/dhcpv4.c maintained its transaction identifier iface-config.dhcpv4.xid as a counter rather than as a per-transaction random value. It was seeded once with sysrand32get in dhcpv4startinternal, incremented by one in dhcpv4senddiscover and dhcpv4senddecline...