northd: Avoid useless iterations when recomputing policies.

When recomputing router policies we can just mark everything that we
already had as "potentially stale", build the new set of parsed policies
and then remove what actually is stale in one go for all router datapaths.

The old code was achieving the same thing but in a very inefficient way.
It used to:
- walk all routers, for each router R:
    - walk all parsed policies (for all routers) and mark as potentially
    stale the ones that correspond to R
    - reparse R's policies (making the ones that are still relevant "not
    stale")
    - remove all actually stale policies for R

But that means O(N x M) iterations, where N is the number of routers and
M is the number of router policies in the NB database.

But it turns out we never had any stale policies because we always do a
recompute of the route_policies node.  So we can remove all the stale
checking and looking up of parsed routes.

This makes it that we can rebuild the parsed policies in a single pass,
with a complexity of O(M).

Some test numbers from a scaled setup, 1.6K routers with a total number
of 4.8K policies:

Before:
    node: route_policies, recompute (forced) took 254ms
After:
    node: route_policies, recompute (forced) took 6ms

Fixes: 15c9c9f ("northd: Add bfd, static_routes, route_policies and bfd_sync nodes to I-P engine.")
Reported-at: https://redhat.atlassian.net/browse/FDP-3996
Assisted-by: Claude Opus 4.6, Claude Code
Acked-by: Ales Musil <amusil@redhat.com>
Signed-off-by: Dumitru Ceara <dceara@redhat.com>
(cherry picked from commit 24ed825)

Author: dceara

northd/northd.c

@@ -14356,12 +14356,6 @@ build_route_policies(struct ovn_datapath *od, const struct hmap *lr_ports,
 {
     struct route_policy *rp;
 
-    HMAP_FOR_EACH (rp, key_node, route_policies) {
-        if (rp->nbr == od->nbr) {
-            rp->stale = true;
-        }
-    }
-
     /* Create chain numeric ids for policies with chain name set */
     for (int i = 0; i < od->nbr->n_policies; i++) {
         const struct nbrec_logical_router_policy *rule = od->nbr->policies[i];
@@ -14441,7 +14435,6 @@ build_route_policies(struct ovn_datapath *od, const struct hmap *lr_ports,
         new_rp->rule = rule;
         new_rp->n_valid_nexthops = n_valid_nexthops;
         new_rp->valid_nexthops = valid_nexthops;
-        new_rp->nbr = od->nbr;
         new_rp->chain_id = chain_id;
         new_rp->jump_chain_id = jump_chain_id;
 
@@ -14450,21 +14443,10 @@ build_route_policies(struct ovn_datapath *od, const struct hmap *lr_ports,
         if (!rp) {
             hmap_insert(route_policies, &new_rp->key_node, hash);
         } else {
-            rp->stale = false;
             free(valid_nexthops);
             free(new_rp);
         }
     }
-
-    HMAP_FOR_EACH_SAFE (rp, key_node, route_policies) {
-        if (!rp->stale) {
-            continue;
-        }
-
-        hmap_remove(route_policies, &rp->key_node);
-        free(rp->valid_nexthops);
-        free(rp);
-    }
 }
 
 /* Logical router ingress table POLICY: Policy.

northd/northd.h

@@ -192,8 +192,6 @@ struct route_policy {
     const struct nbrec_logical_router_policy *rule;
     size_t n_valid_nexthops;
     char **valid_nexthops;
-    const struct nbrec_logical_router *nbr;
-    bool stale;
     uint32_t chain_id;
     uint32_t jump_chain_id;
 };