Changes

iu_client: use new struct osmo_rnc_id

The osmo_rnc_id is a libosmocore type which can be used across
different libraries.
In preparation to notify the SGSN when a new RAC/LAC is learned.

Depends-on: I17a2adedc2c2ab158f40d58280f5df5c6967b8ec (libosmocore)
Change-Id: Id8db70bd3d63b0533b637402a91757eb677c38b7