NR UE: Enable additional PDU session

• fix a bug with wraparound of buffer_remain_ep
• Add --extra-pdu-id command line option

Testing procedure:

1. Start cn in openairinterface5g/doc/tutorial_resources/oai-cn5g with docker compose up
2. Start gnb:

sudo ./nr-softmodem -O ../../targets/PROJECTS/GENERIC-NR-5GC/CONF/gnb.sa.band78.fr1.106PRB.usrpb210.conf --gNBs.[0].min_rxtxtime 6 --rfsim --rfsimulator.server_address server

3. Monitor extra interfaces being created:

watch -n 0.5 "ifconfig | grep tun"

4. Start UE:

sudo ./nr-uesoftmodem -C 3619200000 -r 106 --numerology 1 --ssb 516  --band 78 --rfsim  --uicc0.imsi 001010000000001 --extra-pdu-id 11

5. An extra tun interface oaitun_ue1p11 should be created. Observe in the terminal from step 3
6. Ping the core network from both interfaces, e.g., ping -I oaitun_ue1p11 10.0.0.1, ping -I oaitun_ue1 10.0.0.1. This should generate traffic on the gNB on different LCIDs.