wifi-scripts: fix nested config accumulation in wdev_set_data

wifi-scripts: fix nested config accumulation in wdev_set_data

When storing device-level data, wdev_set_data() spread the entire wdev
object into handler_data. Since handler_config.data is set from the
previous handler_data[wdev.name] before each setup, this created
exponentially growing nesting with each reload, eventually causing
"nesting too deep" JSON parse errors.

Fix by initializing cur to a simple object containing only the device
name instead of the entire wdev object.

Signed-off-by: Felix Fietkau <nbd@nbd.name>