Broadcast message failure

```
Starting smart config pairing procedure
Waiting for the device to install the intermediate firmware
Put device in EZ config mode (blinking fast)
Sending SSID vtrust-flash
Sending wifiPassword
Sending token 00000000
Sending secret 0101
......Traceback (most recent call last):
File "./smartconfig/main.py", line 26, in
smartconfig( passwd, ssid, region, token, secret )
File "/usr/bin/tuya-convert/scripts/smartconfig/smartconfig.py", line 61, in smartconfig
sock.send_broadcast(broadcast_body)
File "/usr/bin/tuya-convert/scripts/smartconfig/smartconfig.py", line 34, in send_broadcast
self._socket.sendto( b'\0' * length, ('255.255.255.255', 30011))
OSError: [Errno 101] Network is unreachable
......................................................................................................................
Timed out while waiting for the device to (re)connect
```
Device: V-TAC 5117

Start with scripts/smartconfig/smartconfig.py, especially send_broadcast, and reproduce the traceback from smartconfig/main.py. Investigate the Errno 101 failure when sending to 255.255.255.255:30011; done means the broadcast step no longer fails and the pairing procedure can proceed past it.

Written by the indexing model from the issue text.