CVE-2026-89561 ipv6: rpl: fix NULL dereference of idev in ipv6_rpl_srh_rcv()

In the Linux kernel, the following vulnerability has been resolved: ipv6: rpl: fix NULL dereference of idev in ipv6rplsrhrcv ipv6rplsrhrcv dereferences idev from in6devget without a NULL check when reading idev-cnf.rplsegenabled. When the device's MTU drops below IPV6MINMTU, addrconfifdown clears...