ofctrl: Fix using uninitialized flow cookie.

ovn-controller has uninitialized flow cookie because ofctrl_dup_flow()
doesn't copy it from the original flow while duplicating.  This could
cause redundant flow updates or other issues.

Valgrind reports:

 Conditional jump or move depends on uninitialised value(s)
    at 0x414B1C: ofctrl_put (ofctrl.c:1192)
    by 0x409ACB: main (ovn-controller.c:2086)
  Uninitialised value was created by a heap allocation
    at 0x483980B: malloc (vg_replace_malloc.c:309)
    by 0x4C8474: xmalloc (util.c:138)
    by 0x414553: ofctrl_dup_flow (ofctrl.c:793)
    by 0x4152CD: ofctrl_put (ofctrl.c:1231)
    by 0x409ACB: main (ovn-controller.c:2086)

Fixes: d25e286 ("ovn-controller: Tie OpenFlow and logical flows using OpenFlow cookie.")
Signed-off-by: Ilya Maximets <i.maximets@ovn.org>
Signed-off-by: Mark Michelson <mmichels@redhat.com>
Acked-by: Dumitru Ceara <dceara@redhat.com>

controller/ofctrl.c

@@ -799,6 +799,7 @@ ofctrl_dup_flow(struct ovn_flow *src)
     dst->sb_uuid = src->sb_uuid;
     dst->match_hmap_node.hash = src->match_hmap_node.hash;
     dst->uuid_hindex_node.hash = uuid_hash(&src->sb_uuid);
+    dst->cookie = src->cookie;
     return dst;
 }