gsup: align ordering of IEs
Align with the IE order produced by libosmocore's GSUP encoder.
Change-Id: I5caa3101da310cddfa311d068ad889bca697b438
Related: 54343caa ("common/gsup.adoc: document Supplementary Services extension")
Related: ce32ec2a ("gsup: Document ePDG Tunnel Req/Res/Err")
Related: 92cf519c ("GSUP: document inter-MSC handover additions")
