CVE-2026-54345: GoPacket's Diameter AVP decoder: uint32 underflow on vendor header size leads to unbounded ~4 GiB allocation (unauthenticated remote DoS)

The Diameter AVP decoder in github.com/gopacket/gopacket computes dataLength := avp.Length - uint32(headerSize) without first ensuring avp.Length >= headerSize. When the Vendor flag is set, headerSize is 12, but the only length guard upstream rejects avp.Length < 8. An AVP with the Vendor flag set and a 24-bit Length field of 8, 9, 10, or 11 therefore underflows the uint32 subtraction to ~4,294,967,292, which is passed straight to make([]byte, dataLength). A single 32-byte Diameter message forces a ~4 GiB allocation; a short burst of such messages exhausts memory and OOM-kills memory-constrained collectors. This is an unauthenticated remote denial of service (CWE-191 integer underflow -> CWE-770 unbounded allocation).