Dont mirror the same packet again

If mirroring is enabled on analyzing VM's port itself, one copy of the
original packet gets mirrored to that port. But this mirrored packet
should not be mirroed again. Right now without verifying whether the
packet is mirrored or not, it is attempted for mirroring again.

When a packet is mirrored it is marked with flag VP_FLAG_FROM_DP. If
this flag is set it is not mirrored again.

Change-Id: Ie4cca916945878b77bc4db7666992f3933db3e13
closes-bug: #1549761

dp-core/vr_mirror.c

@@ -380,6 +380,10 @@ vr_mirror(struct vrouter *router, uint8_t mirror_id,
     struct vr_nexthop *pkt_nh;
     bool reset;
 
+    /* If the packet is already mirrored, dont mirror again */
+    if (pkt->vp_flags & VP_FLAG_FROM_DP)
+        return 0;
+
     mirror = router->vr_mirrors[mirror_id];
     if (!mirror)
         return 0;