ipv6: Change skb->data before using icmpv6_notify() to propagate redirect

In function ndisc_redirect_rcv(), the skb->data points to the transport
header, but function icmpv6_notify() need the skb->data points to the
inner IP packet. So before using icmpv6_notify() to propagate redirect,
change skb->data to point the inner IP packet that triggered the sending
of the Redirect, and introduce struct rd_msg to make it easy.

Signed-off-by: Duan Jiong <djduanjiong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/ndisc.h b/include/net/ndisc.h
index 7af1ea8..23b3a7c 100644
--- a/include/net/ndisc.h
+++ b/include/net/ndisc.h
@@ -78,6 +78,13 @@
 	__be32			retrans_timer;
 };
 
+struct rd_msg {
+	struct icmp6hdr icmph;
+	struct in6_addr	target;
+	struct in6_addr	dest;
+	__u8		opt[0];
+};
+
 struct nd_opt_hdr {
 	__u8		nd_opt_type;
 	__u8		nd_opt_len;