Handle KSI in NAS Registration Request

Related to RAN issue oai/openairinterface5g#818 (closed)

Scenario: The UE goes into RRC IDLE and sends KSI in NAS Registration Request, when connecting again and resulting already registered in the CN:

• the UE deletes a security context, it needs to indicate that to AMF by using NAS key set identifier IE and set the value to no key is available (section 9.11.3.32 NAS key set identifier @ 3GPP TS 24.501 version 16.14.0 ) in the Registration Request message, so that AMF can trigger a new authentication procedure

todo:

• handle KSI in NAS Registration Request
• trigger Authentication Request
• handle Authentication Response
• trigger Security Mode control procedures