usbnet: fix cyclical race on disconnect with work queue

commit 04e90683 upstream.

The work can submit URBs and the URBs can schedule the work.
This cycle needs to be broken, when a device is to be stopped.
Use a flag to do so.
This is a design issue as old as the driver.

Signed-off-by: Oliver Neukum <oneukum@suse.com>
Fixes: 1da177e4 ("Linux-2.6.12-rc2")
CC: stable@vger.kernel.org
Link: https://patch.msgid.link/20240919123525.688065-1-oneukum@suse.com


Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>