netdev: Properly clear 'details' when iterating in NETDEV_QOS_FOR_EACH.

netdev: Properly clear 'details' when iterating in NETDEV_QOS_FOR_EACH.

The function comment for netdev_queue_dump_next() said that it cleared its
'detail' argument, but it didn't actually do that, which meant that details
could be incorrectly carried along from one queue to the next.

Reported-by: Flavio Leitner <fbl@sysclose.org>
Signed-off-by: Ben Pfaff <blp@ovn.org>
Acked-by: Eelco Chaudron <echaudro@redhat.com>
Acked-by: Flavio Leitner <fbl@sysclose.org>