NDIS_FLAGS_DONT_LOOPBACK and NDIS_FLAGS_SKIP_LOOPBACK prevents the packet from being indicated back. However, these flags are OS/NDIS specific. You can see some details here http://www.ndis.com/papers/loopback.htm
You can try using MSTCP_FLAG_LOOPBACK_BLOCK for the adapter you work over. It drops incoming packets if source MAC is the same as local MAC. Regretfully there is no way to prevent packet indication on NT4 at all.