ovn-northd.c: Remove the use of the REGBIT_SKIP_LOOKUP_NEIGHBOR bit.

In LR ingress stage LOOKUP_NEIGHBOR and LEARN_NEIGHBOR, the flag
REGBIT_SKIP_LOOKUP_NEIGHBOR was used to indicate if mac-binding
lookup can be skipped. This patch avoid using the bit by combining
it with the REGBIT_LOOKUP_NEIGHBOR_RESULT bit, and assigning 1
to REGBIT_LOOKUP_NEIGHBOR_RESULT serves same purpose of skipping
the lookup. There will be a new bit needed in a future patch, and
this change can avoid using too many bits unnecessarily.

Acked-by: Numan Siddique <numans@ovn.org>
Signed-off-by: Han Zhou <hzhou@ovn.org>

northd/ovn-northd.8.xml

@@ -1595,7 +1595,7 @@ next;
 
       <li>
         A priority-0 fallback flow that matches all packets and applies
-        the action <code>reg9[3] = 1; next;</code>
+        the action <code>reg9[2] = 1; next;</code>
         advancing the packet to the next table.
       </li>
     </ul>
@@ -1610,17 +1610,14 @@ next;
 
     <p>
       reg9[2] will be <code>1</code> if the <code>lookup_arp/lookup_nd</code>
-      in the previous table was successful.
-    </p>
-
-    <p>
-      reg9[3] will be <code>1</code> if there was no need to do the lookup.
+      in the previous table was successful, or if there was no need to do the
+      lookup.
     </p>
 
     <ul>
       <li>
         A priority-100 flow with the match
-        <code>reg9[2] == 1 || reg9[3] == 1</code> and advances the packet
+        <code>reg9[2] == 1</code> and advances the packet
         to the next table as there is no need to learn the neighbor.
       </li>
 

northd/ovn-northd.c

@@ -222,7 +222,6 @@ enum ovn_stage {
 /* Register to store the result of check_pkt_larger action. */
 #define REGBIT_PKT_LARGER        "reg9[1]"
 #define REGBIT_LOOKUP_NEIGHBOR_RESULT "reg9[2]"
-#define REGBIT_SKIP_LOOKUP_NEIGHBOR "reg9[3]"
 
 /* Register to store the eth address associated to a router port for packets
  * received in S_ROUTER_IN_ADMISSION.
@@ -8475,14 +8474,13 @@ build_lrouter_flows(struct hmap *datapaths, struct hmap *ports,
                       "lookup_nd(inport, ip6.src, nd.sll); next;");
 
         /* For other packet types, we can skip neighbor learning.
-         * So set REGBIT_SKIP_LOOKUP_NEIGHBOR to 1. */
+         * So set REGBIT_LOOKUP_NEIGHBOR_RESULT to 1. */
         ovn_lflow_add(lflows, od, S_ROUTER_IN_LOOKUP_NEIGHBOR, 0, "1",
-                      REGBIT_SKIP_LOOKUP_NEIGHBOR" = 1; next;");
+                      REGBIT_LOOKUP_NEIGHBOR_RESULT" = 1; next;");
 
         /* Flows for LEARN_NEIGHBOR. */
         /* Skip Neighbor learning if not required. */
         ovn_lflow_add(lflows, od, S_ROUTER_IN_LEARN_NEIGHBOR, 100,
-                      REGBIT_SKIP_LOOKUP_NEIGHBOR" == 1 || "
                       REGBIT_LOOKUP_NEIGHBOR_RESULT" == 1", "next;");
 
         ovn_lflow_add(lflows, od, S_ROUTER_IN_LEARN_NEIGHBOR, 90,