[busybox] Enable CONFIG_NC_SERVER, closes #3495

Tested on R-Pi/master. Size of busybox bin increased by 2544 bytes.

With CONFIG_NC_SERVER not set:
```
-rwsr-xr-x    1 root     root        500552 Sep 21 21:30 /bin/busybox
```
With CONFIG_NC_SERVER=Y:
```
-rwsr-xr-x    1 root     root        503096 Sep 22 00:18 /bin/busybox
```

Sending journalctl to a remote syslog server:
```
rpi512:~ # journalctl --follow | nc -u 192.168.0.4 514
```
now works as expected.