net: fix tunnels in netns after ndo_ changes

dev_net_set() should be the very first thing after alloc_netdev().

"ndo_" changes turned simple assignment (which is OK to do before netns
assignment) into quite non-trivial operation (which is not OK, init_net was
used). This leads to incomplete initialisation of tunnel device in netns.

BUG: unable to handle kernel NULL pointer dereference at 00000004
IP: [<c02efdb5>] ip6_tnl_exit_net+0x37/0x4f
*pde = 00000000
Oops: 0000 [#1] PREEMPT DEBUG_PAGEALLOC
last sysfs file: /sys/class/net/lo/operstate

Pid: 10, comm: netns Not tainted (2.6.28-rc6 #1)
EIP: 0060:[<c02efdb5>] EFLAGS: 00010246 CPU: 0
EIP is at ip6_tnl_exit_net+0x37/0x4f
EAX: 00000000 EBX: 00000020 ECX: 00000000 EDX: 00000003
ESI: c5caef30 EDI: c782bbe8 EBP: c7909f50 ESP: c7909f48
 DS: 007b ES: 007b FS: 0000 GS: 0000 SS: 0068
Process netns (pid: 10, ti=c7908000 task=c7905780 task.ti=c7908000)
Stack:
 c03e75e0 c7390bc8 c7909f60 c0245448 c7390bd8 c7390bf0 c7909fa8 c012577a
 00000000 00000002 00000000 c0125736 c782bbe8 c7909f90 c0308fe3 c782bc04
 c7390bd4 c0245406 c084b718 c04f0770 c03ad785 c782bbe8 c782bc04 c782bc0c
Call Trace:
 [<c0245448>] ? cleanup_net+0x42/0x82
 [<c012577a>] ? run_workqueue+0xd6/0x1ae
 [<c0125736>] ? run_workqueue+0x92/0x1ae
 [<c0308fe3>] ? schedule+0x275/0x285
 [<c0245406>] ? cleanup_net+0x0/0x82
 [<c0125ae1>] ? worker_thread+0x81/0x8d
 [<c0128344>] ? autoremove_wake_function+0x0/0x33
 [<c0125a60>] ? worker_thread+0x0/0x8d
 [<c012815c>] ? kthread+0x39/0x5e
 [<c0128123>] ? kthread+0x0/0x5e
 [<c0103b9f>] ? kernel_thread_helper+0x7/0x10
Code: db e8 05 ff ff ff 89 c6 e8 dc 04 f6 ff eb 08 8b 40 04 e8 38 89 f5 ff 8b 44 9e 04 85 c0 75 f0 43 83 fb 20 75 f2 8b 86 84 00 00 00 <8b> 40 04 e8 1c 89 f5 ff e8 98 04 f6 ff 89 f0 e8 f8 63 e6 ff 5b
EIP: [<c02efdb5>] ip6_tnl_exit_net+0x37/0x4f SS:ESP 0068:c7909f48
---[ end trace 6c2f2328fccd3e0c ]---

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>