vrf: Fix IPv6 with qdisc and xfrm

[ Upstream commit a53c102872ad6e34e1518e25899dc9498c27f8b1 ]

When a qdisc is attached to the VRF device, the packet goes down the ndo
xmit function which is setup to send the packet back to the VRF driver
which does a lookup to send the packet out. The lookup in the VRF driver
is not considering xfrm policies. Change it to use ip6_dst_lookup_flow
rather than ip6_route_output.

Fixes: 35402e31 ("net: Add IPv6 support to VRF device")
Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>