Handle F1 Reset at DU, and ensure state re-init on F1Setup

This MR implements the following:

1. F1AP Reset:
   • Initializes the stubs for F1 Reset, both CU and DU.
   • Implementation for F1 Reset handling at the DU, both encoder/ decoder, and handlers.
2. F1SetupRequest:
   • Ensure the UE-related states are always cleared on every F1SetupRequest (especially when DU re-establishes its SCTP connection with the CU).
     • Quoted from TS38.473 8.2.3.2, "This procedure erases any existing application level configuration data in the two nodes and replaces it with the one received. This procedure also re-initializes the F1AP UE-related contexts (if any) and erases all related signaling connections in the two nodes like a Reset procedure would do."
     • Impact: Restarting the CU midway will not result in a crash.

Both (1) and (2) use similar logic in re-init/initializing the UE-related states in the DU, i.e., clear MAC/RLC, F1, and GTP.

HOWEVER, I am not 100% sure whether my interpretation of the standards is correct for the above, i.e., Reset and F1Setup.

So, feedback and discussions are welcome. Thanks!

Important notes:

• F1Reset handling at the DU is currently limited to the entire "f1-Interface", i.e., all states are cleared, "partialF1-interface" still needs to be looked further into which may come in a separate MR later.
• F1Reset handling is not implemented at the CU; neither CU nor DU currently generates/sends out the F1Reset.
• F1Reset handling at the DU is tested using an SCTP proxy in F1-C that generates the F1 Reset messages.

added 5G-NR label

OAI RAN-Container-Parent build (8170): failed (https://jenkins-oai.eurecom.fr/job/RAN-Container-Parent/8170/)

List of failing test stages:

• RAN-NSA-B200-Module-LTEBOX-Container
• RAN-SA-OAIUE-CN5G
• RAN-L2-Sim-Test-5G
• RAN-RF-Sim-Test-5G
• RAN-SA-B200-Module-SABOX-Container

requested review from @schmidtr

changed milestone to %REVIEW_IN_PROGRESS

thanks a lot, that looks like a good start! let me know if you need help to finish this!

added 4 commits

• 3e8f52a1 - Revert "handle null UE in rach when DU reset"
• cfa954ad - handle null UE in rach when DU reset
• fbdf04f8 - Revert "handle null UE in rach when DU reset"
• 7ac94c16 - Handle Msg3 with SRB1 RRCReestablishmentComplete and MAC CE C-RNTI

Compare with previous version

OAI RAN-Container-Parent build (8452): Merge Conflicts -- Cannot perform CI

OAI RAN-Container-Parent build (8452): failed (https://jenkins-oai.eurecom.fr/job/RAN-Container-Parent/8452/)

List of failing test stages:

added 213 commits

• 7ac94c16...1244c9a2 - 204 commits from branch develop
• 6230395c - initial f1ap reset support
• 0c3abc00 - added dedicated method for f1ap_reset on release_ue
• 35af8787 - handle f1reset at du, send reset_ack, fix f1setup
• f429b1b4 - missing present statment
• 9c188062 - fix access to null UE
• d0e1725c - handle RESET_ACK at CU
• abf2aeb4 - fix typo
• 2861d783 - move code that init ue states to mac_rrc_dl_handler, and some cleanup
• 6d5fb8dd - removed nr_mac_release_ue_f1ap_reset and use nr_mac_release_ue

Compare with previous version

@schmidtr, I have (mostly) revised the MR based on the above discussion, and also rebased the MR w.r.t the latest develop branch. Please have a look. Thanks!

changed the description

OAI RAN-Container-Parent build (8453): failed (https://jenkins-oai.eurecom.fr/job/RAN-Container-Parent/8453/)

List of failing test stages:

• RAN-gNB-N300-Timing-Phytest-LDPC
• RAN-RF-Sim-Test-5G
• RAN-NSA-B200-Module-LTEBOX-Container
• RAN-SA-B200-Module-SABOX-Container