ARP response on request interface for service instance

In in-network service instance case, when service scaling
is more than one, all the instances are going to have the
same mac address and IP address. Inet route points to
ECMP composite nexthop but FDB route does not point to ECMP
nexthop. So when ARP request is received from service VM
Vrouter needs to send ARP response on the incoming interface
rather bridging the ARP reply packet, as FDB route points
to arbitrarly any of the service VM encap L2 nexthop.

After preparing the ARP reply packet,bridge lookup is done
and outgoing interface is compared against ingress interface.
If they are not same, reply packet is transmitted on
ingress interface.

Change-Id: Id90228b432e2d86360a7b77d332b7cdb701cf144
closes-bug: #1461882

dp-core/vr_datapath.c

@@ -155,6 +155,9 @@ vr_arp_proxy(struct vr_arp *sarp, struct vr_packet *pkt,
     struct vr_arp *arp;
     struct vr_forwarding_md fmd_new;
     struct vr_interface *vif = pkt->vp_if;
+    struct vr_route_req rt;
+    bool vif_tx = false;
+    struct vr_nexthop *nh;
 
     eth = (struct vr_eth *)pkt_push(pkt, sizeof(*eth));
     if (!eth) {
@@ -186,13 +189,35 @@ vr_arp_proxy(struct vr_arp *sarp, struct vr_packet *pkt,
      * doing vr_bridge_input, we check for the flag NO_ARP_PROXY and
      * and if set, directly send out on that interface
      */
+
+
     if (vif_is_vhost(vif) ||
             (vif->vif_flags & VIF_FLAG_NO_ARP_PROXY)) {
-        vif->vif_tx(vif, pkt, fmd);
+        vif_tx = true;
     } else {
-        vr_bridge_input(vif->vif_router, pkt, &fmd_new);
+
+        rt.rtr_req.rtr_label_flags = 0;
+        rt.rtr_req.rtr_index = VR_BE_INVALID_INDEX;
+        rt.rtr_req.rtr_mac_size = VR_ETHER_ALEN;
+        rt.rtr_req.rtr_mac =(int8_t *) arp->arp_dha;
+        rt.rtr_req.rtr_vrf_id = fmd_new.fmd_dvrf;
+        nh = vr_bridge_lookup(fmd->fmd_dvrf, &rt);
+        if (!nh || !(nh->nh_flags & NH_FLAG_VALID)) {
+            vr_pfree(pkt, VP_DROP_INVALID_NH);
+            return;
+        }
+        if (rt.rtr_req.rtr_label_flags & VR_BE_LABEL_VALID_FLAG)
+            fmd_new.fmd_label = rt.rtr_req.rtr_label;
+
+        if (vif_is_virtual(vif) && (nh->nh_dev != vif)) {
+            vif_tx = true;
+        }
     }
 
+    if (vif_tx)
+        vif->vif_tx(vif, pkt, &fmd_new);
+    else
+        nh_output(pkt, nh, &fmd_new);
     return;
 }