For port mirroring, flow index should not be set

During transmit port mirror, we seem to be using the mirror values
from the flow of the original packet. This is not a right behavior,
since port mirroring shouldn't be depending on flow based mirror
values.

Hence reset the flow index for the port mirrored packet

Change-Id: I1aff969b08a2f247ccf1fc636d6689350e819f29
Closes-Bug: #1636638

dp-core/vr_interface.c

@@ -247,6 +247,7 @@ vif_mirror(struct vr_interface *vif, struct vr_packet *pkt,
     }
 
     mfmd.fmd_dvrf = vif->vif_vrf;
+    mfmd.fmd_flow_index = -1;
 
     if (pkt->vp_type == VP_TYPE_NULL)
         vr_pkt_type(pkt, 0, &mfmd);