The subscriptions to NRF should be tied to the number of NF's and number
of services per NF that we support, instead of number of UE's.
This decreases memory usage of each NF slightly, depending on the
configuration.
After N2 Handover (1 AMF, multiple gNB's) was successfully executed, the
PDU session was not properly released afterwards on PDU Session Release
Request from UE.
The reason was that after N2 Handover the new 'ran_ue' context did not
have any information about the active PDU sessions.
Copy the information about PDU sessions from old ran_ue context to the
new one.
TS23.007 17.4.1
19A PFCP based restart procedures
After a PFCP entity has restarted, it shall immediately update all local Recovery Time Stamps and shall clear all remote
Recovery Time Stamps. When peer PFCP entities information is available, i.e. when the PFCP Association is still alive,
the restarted PFCP entity shall send its updated Recovery Time Stamps in a Heartbeat Request message to the peer
PFCP entities before initiating any PFCP session signalling.
Follow-up on [#2048](https://github.com/open5gs/open5gs/pull/2048)
AMF crashes when 'skipInd' field is missing:
```
amf | 03/21 07:45:04.092: [amf] FATAL: [imsi-001010000000000] No skipInd (../src/amf/namf-handler.c:392)
amf | 03/21 07:45:04.092: [amf] FATAL: amf_namf_comm_handle_n1_n2_message_transfer: should not be reached. (../src/amf/namf-handler.c:393)
```
In case of CM_CONNECTED skipInd is not important.
In case of CM_IDLE the proper relase would contain skipInd.
SMF already handles the freeing in labels correctly.
In the same manner the memsets are moved to the beginning of the
problematic functions in AMF and PCF.
When UDM issues a SDM Data Change Notification with request to modify
RAT restrictions, AMF would crash when it tried to send a SDM
subscription delete as part of Network Initiated Deregistration.
Function amf_ue_sbi_discover_and_send() changed from returning boolean,
to returning integer (one of OGS_OK/OGS_ERROR/...).
When both IPv4 and IPv6 Frame Routes are set, IPv4 Frame Route list
was subsequently cleared.
When UE tried to deregister, PCF would crash when it tried to free the
Frame Routing list.
POST requests to {apiRoot}/nnrf-nfm/v1/subscriptions return
a HTTP Location header in 201 respose
in the form {apiRoot}/nnrf-nfm/v1/subscriptions/{subscriptionID}
In case that handling Service Request results in an error, AMF sends a
Service Reject and sets UE's context to exception state. Without the
'break', the code would set UE's context to registered state.
