IPoIB: Fix build now that neighbour destructor is in neigh_params

Fix the IPoIB build (which is broken in net-2.6.17 because of my
screw-up, which left out this chunk in ipoib_multicast.c). 
The neighbour destructor is now in neigh_params, so we don't
need to clear it in the ops structure.
Signed-off-by: NRoland Dreier <rolandd@cisco.com>

drivers/infiniband/ulp/ipoib/ipoib_multicast.c

@@ -115,7 +115,6 @@ static void ipoib_mcast_free(struct ipoib_mcast *mcast)
 		if (neigh->ah)
 			ipoib_put_ah(neigh->ah);
 		*to_ipoib_neigh(neigh->neighbour) = NULL;
-		neigh->neighbour->ops->destructor = NULL;
 		kfree(neigh);
 	}