XFRM,IPv6: initialize ip6_dst_blackhole_ops.kmem_cachep

ip6_dst_blackhole_ops.kmem_cachep is not expected to be NULL (i.e. to
be initialized) when dst_alloc() is called from ip6_dst_blackhole().
Otherwise, it results in the following (xfrm_larval_drop is now set to
1 by default):

[   78.697642] Unable to handle kernel paging request for data at address 0x0000004c
[   78.703449] Faulting instruction address: 0xc0097f54
[   78.786896] Oops: Kernel access of bad area, sig: 11 [#1]
[   78.792791] PowerMac
[   78.798383] Modules linked in: btusb usbhid bluetooth b43 mac80211 cfg80211 ehci_hcd ohci_hcd sungem sungem_phy usbcore ssb
[   78.804263] NIP: c0097f54 LR: c0334a28 CTR: c002d430
[   78.809997] REGS: eef19ad0 TRAP: 0300   Not tainted  (2.6.27-rc5)
[   78.815743] MSR: 00001032 <ME,IR,DR>  CR: 22242482  XER: 20000000
[   78.821550] DAR: 0000004c, DSISR: 40000000
[   78.827278] TASK = eef0df40[3035] 'mip6d' THREAD: eef18000
[   78.827408] GPR00: 00001032 eef19b80 eef0df40 00000000 00008020 eef19c30 00000001 00000000
[   78.833249] GPR08: eee5101c c05a5c10 ef9ad500 00000000 24242422 1005787c 00000000 1004f960
[   78.839151] GPR16: 00000000 10024e90 10050040 48030018 0fe44150 00000000 00000000 eef19c30
[   78.845046] GPR24: eef19e44 00000000 eef19bf8 efb37c14 eef19bf8 00008020 00009032 c0596064
[   78.856671] NIP [c0097f54] kmem_cache_alloc+0x20/0x94
[   78.862581] LR [c0334a28] dst_alloc+0x40/0xc4
[   78.868451] Call Trace:
[   78.874252] [eef19b80] [c03c1810] ip6_dst_lookup_tail+0x1c8/0x1dc (unreliable)
[   78.880222] [eef19ba0] [c0334a28] dst_alloc+0x40/0xc4
[   78.886164] [eef19bb0] [c03cd698] ip6_dst_blackhole+0x28/0x1cc
[   78.892090] [eef19be0] [c03d9be8] rawv6_sendmsg+0x75c/0xc88
[   78.897999] [eef19cb0] [c038bca4] inet_sendmsg+0x4c/0x78
[   78.903907] [eef19cd0] [c03207c8] sock_sendmsg+0xac/0xe4
[   78.909734] [eef19db0] [c03209e4] sys_sendmsg+0x1e4/0x2a0
[   78.915540] [eef19f00] [c03220a8] sys_socketcall+0xfc/0x210
[   78.921406] [eef19f40] [c0014b3c] ret_from_syscall+0x0/0x38
[   78.927295] --- Exception: c01 at 0xfe2d730
[   78.927297]     LR = 0xfe2d71c
[   78.939019] Instruction dump:
[   78.944835] 91640018 9144001c 900a0000 4bffff44 9421ffe0 7c0802a6 bf810010 7c9d2378
[   78.950694] 90010024 7fc000a6 57c0045e 7c000124 <83e3004c> 8383005c 2f9f0000 419e0050
[   78.956464] ---[ end trace 05fa1ed7972487a1 ]---

As commented by Benjamin Thery, the bug was introduced by
f2fc6a54, while adding network
namespaces support to ipv6 routes.

Signed-off-by: Arnaud Ebalard <arno@natisbad.org>
Acked-by: Benjamin Thery <benjamin.thery@bull.net>
Signed-off-by: David S. Miller <davem@davemloft.net>