ipv6: don't call addrconf_dst_alloc again when enable lo
ipv6: don't call addrconf_dst_alloc again when enable lo

If we disable all of the net interfaces, and enable
un-lo interface before lo interface, we already allocated
the addrconf dst in ipv6_add_addr. So we shouldn't allocate
it again when we enable lo interface.

Otherwise the message below will be triggered.
unregister_netdevice: waiting for sit1 to become free. Usage count = 1

This problem is introduced by commit 25fb6ca4ed9cad72f14f61629b68dc03c0d9713f
"net IPv6 : Fix broken IPv6 routing table after loopback down-up"

Signed-off-by: Gao feng <7e9c653c8ec3abfdd967a0616fd143ca77e7b405@cn.fujitsu.com>
Signed-off-by: David S. Miller <fe08d3c717adf2ae63592e4c9aec6e3e404d8e3e@davemloft.net>

KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas