tbf_dl_fsm: Fix '{FLOW}: Event ASSIGN_PCUIF_CNF not permitted'

As seen during manual testing:
20230628140439674 DTBF tbf_dl.cpp:116 MS(IMSI-901700000015256:TLLI-0xd4d57c9d:TA-0:MSCLS-12-12) Allocating DL TBF
...
20230628140439674 DTBFDL tbf_dl.cpp:489 DL_TBF(DL:TFI-0-0-0:E:IMSI-901700000015256:TLLI-0xd4d57c9d){NEW}: Received Event ASSIGN_ADD_CCCH
20230628140439674 DTBFDL bts.cpp:1108 TBF(DL:TFI-0-0-0:E:IMSI-901700000015256:TLLI-0xd4d57c9d){ASSIGN} Tx CCCH (PCH) Immediate Assignment [PktDlAss=PDCH(bts=0,trx=0,ts=5)] TA=0
...
20230628140440238 DMS pdch.cpp:681 MS(IMSI-901700000015256:TLLI-0xd4d57c9d:TA-0:MSCLS-12-12:DL): + rcv_resource_request: now used by 2 (tbf,rcv_resource_request)
20230628140440238 DTBFDL pdch.cpp:738 TBF(DL:TFI-0-0-0:E:IMSI-901700000015256:TLLI-0xd4d57c9d){ASSIGN} Got PACKET RESOURCE REQ while DL-TBF pending, killing it
20230628140440238 DTBF tbf.cpp:271 TBF(DL:TFI-0-0-0:E:IMSI-901700000015256:TLLI-0xd4d57c9d){ASSIGN} free
...
20230628140440377 DTBFUL tbf_ul_fsm.c:169 UL_TBF(UL:TFI-0-0-0:E:IMSI-901700000015256:TLLI-0xd4d57c9d){ASSIGN}: state_chg to FLOW
20230628140440377 DTBF tbf_dl.cpp:116 MS(IMSI-901700000015256:TLLI-0xd4d57c9d:TA-0:MSCLS-12-12:UL) Allocating DL TBF
20230628140440377 DTBFDL tbf_dl.cpp:475 DL_TBF(DL:TFI-0-0-0:E:IMSI-901700000015256:TLLI-0xd4d57c9d){NEW}: Received Event ASSIGN_ADD_PACCH
20230628140440387 DTBF tbf_dl_ass_fsm.c:105 TBF(UL:TFI-0-0-0:E:IMSI-901700000015256:TLLI-0xd4d57c9d){FLOW} start Packet Downlink Assignment (PACCH) for TBF(DL:TFI-0-0-0:E:IMSI-901700000015256:TLLI-0xd4d57c9d){ASSIGN}
...
20230628140440816 DTBFDL bts.cpp:737 DL_TBF(DL:TFI-0-0-0:E:IMSI-901700000015256:TLLI-0xd4d57c9d){FLOW}: Received Event ASSIGN_PCUIF_CNF
20230628140440816 DTBFDL bts.cpp:737 DL_TBF(DL:TFI-0-0-0:E:IMSI-901700000015256:TLLI-0xd4d57c9d){FLOW}: Event ASSIGN_PCUIF_CNF not permitted

Change-Id: I042b0117552acae25c750e762f5cc254399da64f
---
M src/tbf_dl_fsm.c
1 file changed, 42 insertions(+), 0 deletions(-)