ovn-controller: Datapath based conntrack zone for load-balancing.

ovn-controller: Datapath based conntrack zone for load-balancing.

Currently ct_lb() logical action is only added for a logical switch and
we use the conntrack zone allocated for the logical port.  A future commit
will use ct_lb() for a logical router too.  In that case, use the allocated
DNAT zone.

Rationale for not passing zone as an argument for ct_lb():
One way to look at it would be that a "zone" is an internal implementation
detail and should not be seen in a action of logical flow.  But we can then
say that we could rename "zone" as "datapath" in the logical action.  But,
then we would be limiting it to 2 anyway (datapath=lswitch or
datapath=lrouter) - in which case we are inferring it with the current patch.

Signed-off-by: Gurucharan Shetty <guru@ovn.org>
Acked-by: Ben Pfaff <blp@ovn.org>