This reverts commit 4cda7527
from net-next.

Brown bag time.

Michal noticed that this change doesn't work at all when
netif_set_real_num_tx_queues() gets called prior to an initial
dev_activate(), as for instance igb does.

Doing so dies with:

[   40.579142] BUG: kernel NULL pointer dereference, address: 0000000000000400
[   40.586922] #PF: supervisor read access in kernel mode
[   40.592668] #PF: error_code(0x0000) - not-present page
[   40.598405] PGD 0 P4D 0
[   40.601234] Oops: 0000 [#1] PREEMPT SMP PTI
[   40.605909] CPU: 18 PID: 1681 Comm: wickedd Tainted: G            E     5.6.0-rc3-ethnl.50-default #1
[   40.616205] Hardware name: Intel Corporation S2600CP/S2600CP, BIOS RMLSDP.86I.R3.27.D685.1305151734 05/15/2013
[   40.627377] RIP: 0010:qdisc_hash_add.part.22+0x2e/0x90
[   40.633115] Code: 00 55 53 89 f5 48 89 fb e8 2f 9b fb ff 85 c0 74 44 48 8b 43 40 48 8b 08 69 43 38 47 86 c8 61 c1 e8 1c 48 83 e8 80 48 8d 14 c1 <48> 8b 04 c1 48 8d 4b 28 48 89 53 30 48 89 43 28 48 85 c0 48 89 0a
[   40.654080] RSP: 0018:ffffb879864934d8 EFLAGS: 00010203
[   40.659914] RAX: 0000000000000080 RBX: ffffffffb8328d80 RCX: 0000000000000000
[   40.667882] RDX: 0000000000000400 RSI: 0000000000000000 RDI: ffffffffb831faa0
[   40.675849] RBP: 0000000000000000 R08: ffffa0752c8b9088 R09: ffffa0752c8b9208
[   40.683816] R10: 0000000000000006 R11: 0000000000000000 R12: ffffa0752d734000
[   40.691783] R13: 0000000000000008 R14: 0000000000000000 R15: ffffa07113c18000
[   40.699750] FS:  00007f94548e5880(0000) GS:ffffa0752e980000(0000) knlGS:0000000000000000
[   40.708782] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   40.715189] CR2: 0000000000000400 CR3: 000000082b6ae006 CR4: 00000000001606e0
[   40.723156] Call Trace:
[   40.725888]  dev_qdisc_set_real_num_tx_queues+0x61/0x90
[   40.731725]  netif_set_real_num_tx_queues+0x94/0x1d0
[   40.737286]  __igb_open+0x19a/0x5d0 [igb]
[   40.741767]  __dev_open+0xbb/0x150
[   40.745567]  __dev_change_flags+0x157/0x1a0
[   40.750240]  dev_change_flags+0x23/0x60

[...]

Fixes: 4cda7527 ("net: sched: make newly activated qdiscs visible")
Reported-by: Michal Kubecek <mkubecek@suse.cz>
CC: Michal Kubecek <mkubecek@suse.cz>
CC: Eric Dumazet <edumazet@google.com>
CC: Jamal Hadi Salim <jhs@mojatatu.com>
CC: Cong Wang <xiyou.wangcong@gmail.com>
CC: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>