We need to release idev->lcok before we call addrconf_dad_stop().
It calls ipv6_addr_del(), which will hold idev->lock.

Bug spotted by Yasuyuki KOZAKAI <yasuyuki.kozakai@toshiba.co.jp>.
Signed-off-by: NYOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>