Improve SCTP decoding
Add decoding of SCTP INIT chunks
Add decoding of SCTP ACK chunks
Fix decoding SCTP chunk parameters with variable length
Fix decoding SCTP chunk IPv6 parameter
Return empty list in case of absence of SCTP chunks
Add decoding of SCTP HEARTBEAT chunks
Add decoding of SCTP COOKIE ECHO chunks
Add decoding of SCTP COOKIE ACK chunks
Add decoding of SCTP SHUTDOWN, SHUTDOWN ACK and SHUTDOWN COMPLETE chunks
Add decoding of ABORT SCTP chunks
Add decoding of SCTP SACK chunks
Add tests for SCTP
Add tests for SCTP SHUTDOWN chunks