[IPV6] NDISC: Don't rely on node-type hint from L2 unless required.

Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index e10e55c..e517701 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -313,7 +313,9 @@
 	__u16			tc_verd;	/* traffic control verdict */
 #endif
 #endif
+#ifdef CONFIG_IPV6_NDISC_NODETYPE
 	__u8			ndisc_nodetype:2;
+#endif
 	/* 14 bit hole */
 
 #ifdef CONFIG_NET_DMA