IPv6: Complete IPV6_DONTFRAG support

Finally add support to detect a local IPV6_DONTFRAG event
and return the relevant data to the user if they've enabled
IPV6_RECVPATHMTU on the socket.  The next recvmsg() will
return no data, but have an IPV6_PATHMTU as ancillary data.

Signed-off-by: Brian Haley <brian.haley@hp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/ipv6.h b/include/linux/ipv6.h
index 1976942..2ab5509 100644
--- a/include/linux/ipv6.h
+++ b/include/linux/ipv6.h
@@ -257,6 +257,7 @@
 };
 
 #define IP6CB(skb)	((struct inet6_skb_parm*)((skb)->cb))
+#define IP6CBMTU(skb)	((struct ip6_mtuinfo *)((skb)->cb))
 
 static inline int inet6_iif(const struct sk_buff *skb)
 {
@@ -366,6 +367,7 @@
 
 	struct ipv6_txoptions	*opt;
 	struct sk_buff		*pktoptions;
+	struct sk_buff		*rxpmtu;
 	struct {
 		struct ipv6_txoptions *opt;
 		u8 hop_limit;