northd: Don't add lr_out_delivery default drop flow for each lrp.

The default drop flow in lr_out_delivery stage is generated
for every router port of a logical router.  This results in the
lflow_table_add_lflow() to be called multiple times for the
same match and actions and the ovn_lflow to have multiple
dp_refcnts.  Fix this by generating this lflow only once for
each router.

Fixes: 27a92cc ("northd: make default drops explicit")
Acked-by: Han Zhou <hzhou@ovn.org>
Acked-by: Dumitru Ceara <dceara@redhat.com>
Signed-off-by: Numan Siddique <numans@ovn.org>
(cherry picked from commit ada1508)

northd/northd.c

@@ -13470,9 +13470,6 @@ build_egress_delivery_flows_for_lrouter_port(
     ds_put_format(match, "outport == %s", op->json_key);
     ovn_lflow_add(lflows, op->od, S_ROUTER_OUT_DELIVERY, 100,
                   ds_cstr(match), "output;", lflow_ref);
-
-    ovn_lflow_add_default_drop(lflows, op->od, S_ROUTER_OUT_DELIVERY,
-                               lflow_ref);
 }
 
 static void
@@ -14838,9 +14835,9 @@ lrouter_check_nat_entry(const struct ovn_datapath *od,
 }
 
 /* NAT, Defrag and load balancing. */
-static void build_lr_nat_defrag_and_lb_default_flows(struct ovn_datapath *od,
-                                                struct lflow_table *lflows,
-                                                struct lflow_ref *lflow_ref)
+static void build_lr_nat_defrag_and_lb_default_flows(
+    struct ovn_datapath *od, struct lflow_table *lflows,
+    struct lflow_ref *lflow_ref)
 {
     ovs_assert(od->nbr);
 
@@ -15592,6 +15589,11 @@ build_lswitch_and_lrouter_iterate_by_lr(struct ovn_datapath *od,
 
     build_lr_nat_defrag_and_lb_default_flows(od, lsi->lflows, NULL);
     build_lrouter_lb_affinity_default_flows(od, lsi->lflows, NULL);
+
+    /* Default drop rule in lr_out_delivery stage.  See
+     * build_egress_delivery_flows_for_lrouter_port() which adds a rule
+     * for each router port. */
+    ovn_lflow_add_default_drop(lsi->lflows, od, S_ROUTER_OUT_DELIVERY, NULL);
 }
 
 /* Helper function to combine all lflow generation which is iterated by logical