commit 5188cd44 upstream.

UFO is now disabled on all drivers that work with virtio net headers,
but userland may try to send UFO/IPv6 packets anyway.  Instead of
sending with ID=0, we should select identifiers on their behalf (as we
used to).
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Fixes: 916e4cf4 ("ipv6: reuse ip6_frag_id from ip6_ufo_append_data")
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: For 3.2, net/ipv6/output_core.c is a completely new file]
Signed-off-by: Zefan Li <lizefan@huawei.com>