gopacket: SCTP chunk sub-decoder out-of-bounds panics on crafted segments

Summary gopacket decodes SCTP IP protocol 132 by walking the chunk chain through per-chunk-type decoder functions decodeSCTPInit, decodeSCTPShutdown, decodeSCTPError, decodeSCTPSack, in layers/sctp.go. Each of these reads fixed-size header fields and runs count-driven loops without validating the...