1.) Shutdown fix which allows us to see who requested to abort the simulation
2.) Properly initializing the NAS layer which previously was not happening for our simulation mode 5
3.) Changes in configurations to support the EPC(Have Melissa Verify these)

Look only at the last `max_depth` items on the queue, at most.

Episys/andrew+mc/tx pdu list change+dl config req dropping

See merge request aburger/openairinterface5g!5

To match emane.

Checked with:
```
ps ax -o pid,class,priority,comm |grep RR
```

Synchronized with emane.git's implementation of this code which
includes a unit test.

This commit also fixes two bugs in unqueue_matching and one inb
unqueue:

- unqueue_matching was returning the wrong pointer when
  there was no match

- both unqueue_matching and unqueue were not clearing the vacated
  queue entry after removing the item

```
$ ps -eL -o pid,lwp,class,priority,comm | grep -E softmodem|oai:'
 6500  6500 RR  -80 lte-softmodem
 6500  6520 RR  -80 oai:enb-L1-rx
 6500  6522 RR  -80 oai:enb-L1-tx
 6508  6508 RR  -80 lte-uesoftmodem
 6508  6537 RR  -80 oai:ue-phy
 6508  6538 RR  -80 oai:ue-stand
 6509  6509 RR  -80 lte-uesoftmodem
$
```

Episys/andrew/dropping dl config req and tx req

See merge request aburger/openairinterface5g!3

To match emane.

Checked with:
```
ps ax -o pid,class,priority,comm |grep RR
```

Episys/andrew/ul config req filtering

See merge request aburger/openairinterface5g!2

To match emane.

Checked with:
```
ps ax -o pid,class,priority,comm |grep RR
```

This change is to enable use of gprof which requires the process
call `exit` to write out the collected data.

The UE (lte-uesoftmodem) exits cleanly, but the eNB
(lte-softmodem) crashes as it tries to shut down...

Found by valgrind

Found by valgrind

Found by valgrind.

Found by valgrind.

Episys/andrew/msg4 reception failure

See merge request aburger/openairinterface5g!1

Episys/andrew/debugging rach+fixing rx unpack

See merge request aburger/openairinterface5g!4