USB_NETWORK_DISABLED=yes

Setting `USB_NETWORK_DISABLED=yes` in `/etc/default/bbb-boot` is not handled in `/opt/scripts/boot/bbai.sh`

```bash
# workaround for /opt/scripts/boot/bbai.sh
364 if [ ! "x${USB_NETWORK_DISABLED}" = "xyes" ] ; then
365 echo "${log} Starting usb0 network"
366 # Auto-configuring the usb0 network interface:
367 if [ -f /usr/bin/autoconfigure_usb0.sh ] ; then
368 /usr/bin/autoconfigure_usb0.sh || true
369 else
370 #Old Path... 2020.02.25
371 $(dirname $0)/autoconfigure_usb0.sh || true
372 fi
373
374 echo "${log} Starting usb1 network"
375 # Auto-configuring the usb1 network interface:
376 if [ -f /usr/bin/autoconfigure_usb1.sh ] ; then
377 /usr/bin/autoconfigure_usb1.sh || true
378 else
379 #Old Path... 2020.02.25
380 $(dirname $0)/autoconfigure_usb1.sh || true
381 fi
382 fi
```

Not sure if this is the only section, but it prevents starting autoconfigure_usbX.sh

Start by reading /opt/scripts/boot/bbai.sh around the USB network startup section and compare it with the USB_NETWORK_DISABLED=yes setting in /etc/default/bbb-boot. Check how autoconfigure_usb0.sh and autoconfigure_usb1.sh are invoked. Done means the setting is respected and the autoconfigure_usbX.sh scripts are not started when it is enabled.

Written by the indexing model from the issue text.