Changes

GSUP: add missing Current RAT Type IE

This IE has been introduced here:
https://gerrit.osmocom.org/c/libosmocore/+/12452

Used only by osmo_dia2gsup so far:
https://gitea.osmocom.org/erlang/osmo_dia2gsup/commit/388d387dcc9a565b82c709d3b290c734a64ff2a7

Change-Id: Iba841856806b7dbd4b6aa3675e0cc6dff2485da0