ovn-northd: Ensure that flows are added to correct types of datapaths.
A DP_TYPE_SWITCH_* flow should only be added to a logical switch datapath,
and a DP_TYPE_ROUTER_* flow should only be added to a logical router
datapath, but the code previously did not verify this and it caused a
problem in practice.
Suggested-by: Guru Shetty <guru@ovn.org>
Suggested-at: http://openvswitch.org/pipermail/dev/2016-July/075557.html Signed-off-by: Ben Pfaff <blp@ovn.org>