The assumption that dest af is equal to service af is now unreliable, so we
must specify it manually so as not to copy just the first 4 bytes of a v6
address or doing an illegal read of 16 butes on a v6 address.

We "lie" in two places: for synchronization (which we will explicitly
disallow from happening when we have heterogeneous pools) and for black
hole addresses where there's no real dest.
Signed-off-by: Alex Gartrell <agartrell@fb.com>
Acked-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: Simon Horman <horms@verge.net.au>