SCTP: Missing break in switch (CID 1135556)

Change-Id: I00939bb9699493fe7af21497d9e9c013cc3d2e62
Reviewed-on: https://code.wireshark.org/review/5650
Reviewed-by: Jeff Morriss <jeff.morriss.ws@gmail.com>
Reviewed-by: Anders Broman <a.broman58@gmail.com>