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).