northd: Fix incorrect memory allocation for router group datapaths.

We need to allocate memory for 'n_router_dps' pointers, but the
current code allocates space for 'n_router_dps' datapaths, which
is 762 byte structure.  Having 5000 routers in the OpenStack
setup, we allocate 762 * 5000 * 5000 ~= 17 GB of memory instead
of 190 MB:

 98.17% (19,962,746,247B) (heap allocation functions)
 ->90.67% (18,436,818,400B) xcalloc__ (util.c:124)
  ->90.67% (18,436,818,400B) xcalloc (util.c:161)
   ->90.67% (18,436,818,400B) build_lrouter_groups (northd.c:8707)
    ->90.67% (18,436,818,400B) ovnnb_db_run (northd.c:17611)
     ->90.67% (18,436,818,400B) en_northd_run (en-northd.c:137)
      ->90.67% (18,436,818,400B) engine_recompute (inc-proc-eng.c:415)
       ->90.67% (18,436,818,400B) engine_run_node (inc-proc-eng.c:477)
        ->90.67% (18,436,818,400B) engine_run (inc-proc-eng.c:528)
         ->90.67% (18,436,818,400B) inc_proc_northd_run (inc-proc-northd.c:316)
          ->90.67% (18,436,818,400B) main (ovn-northd.c:937)

Also, even though this doesn't affect the allocation size, the order
of arguments is incorrect.

Fix that by using correct pointers and order.  That saves a huge
amount of memory as well as time on allocating and zeroing it out.
In my testing northd node saved 10 seconds on these allocations.

Fixes: b82d351 ("ovn: Add generic HA chassis group")
Signed-off-by: Ilya Maximets <i.maximets@ovn.org>
Acked-by: Mark Michelson <mmichels@redhat.com>
Signed-off-by: Mark Michelson <mmichels@redhat.com>

northd/northd.c

@@ -8027,7 +8027,8 @@ build_lrouter_groups(struct hmap *lr_ports, struct ovs_list *lr_list)
             od->lr_group = xzalloc(sizeof *od->lr_group);
             /* Each logical router group can have max
              * 'n_router_dps'. So allocate enough memory. */
-            od->lr_group->router_dps = xcalloc(sizeof *od, n_router_dps);
+            od->lr_group->router_dps =
+                xcalloc(n_router_dps, sizeof *od->lr_group->router_dps);
             od->lr_group->router_dps[0] = od;
             od->lr_group->n_router_dps = 1;
             sset_init(&od->lr_group->ha_chassis_groups);