Do not try to form flow keys for packets from 'vhost' interface

Currently, fragments from 'vhost' interface undergo fragment table
lookup in an attempt to generate the flow key, which is unnecessary.
Since the head doesn't undergo flow table lookup and hence no fragment
table addition, lookups for subsequent fragments in the fragment table,
in an attempt to generate flow key, will fail and thus packets are
dropped. To, prevent this, never subject packets from vhost (and from
other interfaces on whom policy is disabled) to flow key formation
procedure.

Change-Id: If25a3f0d5cb329fce6341af0e9168ddfb97ef73c
Closes-BUG: #1440680

dp-core/vr_proto_ip.c

@@ -926,9 +926,17 @@ vr_inet_flow_lookup(struct vrouter *router, struct vr_packet *pkt,
     if (pkt->vp_flags & VP_FLAG_FLOW_SET)
         return FLOW_FORWARD;
 
-    ret = vr_inet_form_flow(router, fmd->fmd_dvrf, pkt, fmd->fmd_vlan, flow_p);
-    if (ret < 0)
-        return FLOW_CONSUMED;
+    /*
+     * if the interface is policy enabled, or if somebody else (eg:nexthop)
+     * has requested for a policy lookup, packet has to go through a lookup
+     */
+    if ((pkt->vp_if->vif_flags & VIF_FLAG_POLICY_ENABLED) ||
+            (pkt->vp_flags & VP_FLAG_FLOW_GET)) {
+        lookup = true;
+    }
+
+    if (!lookup)
+        return FLOW_FORWARD;
 
     /* no flow lookup for multicast or broadcast ip */
     if (IS_BMCAST_IP(ip->ip_daddr)) {
@@ -939,25 +947,17 @@ vr_inet_flow_lookup(struct vrouter *router, struct vr_packet *pkt,
         return FLOW_FORWARD;
     }
 
-    /*
-     * if the interface is policy enabled, or if somebody else (eg:nexthop)
-     * has requested for a policy lookup, packet has to go through a lookup
-     */
-    if ((pkt->vp_if->vif_flags & VIF_FLAG_POLICY_ENABLED) ||
-            (pkt->vp_flags & VP_FLAG_FLOW_GET)) {
-        lookup = true;
-    }
+    ret = vr_inet_form_flow(router, fmd->fmd_dvrf, pkt, fmd->fmd_vlan, flow_p);
+    if (ret < 0)
+        return FLOW_CONSUMED;
 
-    if (lookup) {
-        if (vr_ip_fragment_head(ip)) {
-            vr_fragment_add(router, fmd->fmd_dvrf, ip, flow_p->flow4_sport,
-                    flow_p->flow4_dport);
-        }
 
-        return vr_flow_lookup(router, flow_p, pkt, fmd);
+    if (vr_ip_fragment_head(ip)) {
+        vr_fragment_add(router, fmd->fmd_dvrf, ip, flow_p->flow4_sport,
+                flow_p->flow4_dport);
     }
 
-    return FLOW_FORWARD;
+    return vr_flow_lookup(router, flow_p, pkt, fmd);
 }
 
 mac_response_t