Handling the case of not configuring "Ecmp configurable hash"

The previous changes for configurable hash support in Vrouter
(https://review.opencontrail.org/#/c/23922/) has an issue where
if the configurable hash is not configiured, flow key would be
chosen as NULL. As a fix, in no configirable hash is present in
Ecmp NH addition all keys are added.

Change-Id: Id904b25a17c69d931065f25f544e923757187774
partial-bug: #1616814

dp-core/vr_nexthop.c

@@ -636,7 +636,7 @@ nh_ecmp_store_ecmp_config_hash(vr_nexthop_req *req, struct vr_nexthop *nh)
     }
 
     if (!req || !req->nhr_ecmp_config_hash) {
-        nh->nh_ecmp_config_hash = 0;
+        nh->nh_ecmp_config_hash = ((VR_FLOW_KEY_ALL << 8) & 0xFF00);
         return;
     }