This commit introduces several enhancements in X2AP and RRC to deal
with ENDC. The main goal is to deal with UE's on/off and with various
errors.
The following work is included:
- DC prep and DC overall X2 timers
- X2 messages for UE release and DC timers' timeout
Open problems:
- what to do when the UE sends an scg Failure? This commit removes
the UE. And this removal may not be correctly done
- UE removal in the gNB's PHY layer (a next commit is coming,
but it is hackish and will need a rework)
This commits isolates the S1 UE Ctxt Rel Complete and GTP Tunnel Delete
Requests in functions and calls these function in the original place
(rrc_rx_tx()). The same functions are then used in the F1 UE Ctxt Rel
Complete handler to perform the same functionality, i.e. forward the UE
Ctxt Rel Complete message to the MME and free outstanding resources (RRC
context, GTP tunnels, S1 context).