netdev: Fix deadlock when netdev_dump_queues() callback calls into netdev.
We have a call chain like this:
iface_configure_qos() calls
netdev_dump_queues(), which calls
netdev_linux_dump_queues(), which calls back through 'cb' to
qos_unixctl_show_cb(), which calls
netdev_delete_queue(), which calls
netdev_linux_delete_queue().
Both netdev_dump_queues() and netdev_linux_delete_queue() take the same
mutex in the same netdev, which deadlocks.
This commit fixes the problem by getting rid of the callback.
netdev_linux_dump_queue_stats() would benefit from the same treatment but
it's less urgent because I don't see any callbacks from that function that
call back into a netdev function.
Bug #19319. Reported-by: Scott Hendricks <shendricks@vmware.com> Signed-off-by: Ben Pfaff <blp@nicira.com>