net: usb: usbnet: fix race in probe failure

The same bug as in the disconnect code path also exists
in the case of a failure late during the probe process.
The flag must also be set.

Signed-off-by: Oliver Neukum <oneukum@suse.com>
Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Link: https://patch.msgid.link/20241010131934.1499695-1-oneukum@suse.com


Signed-off-by: Paolo Abeni <pabeni@redhat.com>