According to TS 38.413:
* AMBR is conditional to PDU Session Resource to setup in the Initial UE
Context Setup procedure
* The UE Aggregate Maximum Bit Rate IE should be sent to the NG-RAN node
if the AMF has not sent it previously. If it is included in the PDU
SESSION RESOURCE SETUP REQUEST message, the NG-RAN node shall store
it in the UE context
* Range is INTEGER [0..4,000,000,000,000]
To this purpose, changes in the commit:
* Init AMBR to out of range value when creating UE context
* Store AMBR in UE context whenever is received
* Assert if not set at the time of Bearer Setup (should be known at that stage)