vxlan: changelink: Delete remote after update

If a change in remote address prompts a change in a default FDB entry,
that change might be vetoed. If that happens, it would then be necessary
to reinstate the already-removed default FDB entry corresponding to the
previous remote address.

Instead, arrange to have the previous address removed only after the
FDB is successfully vetted.

Signed-off-by: Petr Machata <petrm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>