CVE-2026-5265 Ovn: ovn: heap over-read in icmp error response generation

When generating an ICMP Destination Unreachable or Packet Too Big response, the handler copies a portion of the original packet into the ICMP error body using the IP header's self-declared total length iptotlen for IPv4, ip6plen for IPv6 without validating it against the actual packet buffer size...