In the Initial Context Setup message, the NGAP forwards the AMF UE ID,
but not in the DL NAS Message, although 38.413 says, in $8.3.1.2 either

> The NG-RAN node shall use the AMF UE NGAP ID IE and RAN UE NGAP ID IE
> received in the INITIAL CONTEXT SETUP REQUEST message as identification
> of the logical connection

or in $8.6.2.2

> The NG-RAN node shall use the AMF UE NGAP ID IE and RAN UE NGAP ID IE
> received in the DOWNLINK NAS TRANSPORT message as identification of the
> logical connection

So forward in both cases for harmonization.