[UDP]: Make use of inet_iif() when doing socket lookups.

UDP currently uses skb->dev->ifindex which may provide the wrong
information when the socket bound to a specific interface.
This patch makes inet_iif() accessible to UDP and makes UDP use it.

The scenario we are trying to fix is when a client is running on
the same system and the server and both client and server bind to
a non-loopback device.

Signed-off-by: Vlad Yasevich <vladislav.yasevich@hp.com>
Acked-by: David L Stevens <dlstevens@us.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/inet_sock.h b/include/net/inet_sock.h
index 62daf21..70013c5 100644
--- a/include/net/inet_sock.h
+++ b/include/net/inet_sock.h
@@ -24,6 +24,7 @@
 #include <net/flow.h>
 #include <net/sock.h>
 #include <net/request_sock.h>
+#include <net/route.h>
 
 /** struct ip_options - IP Options
  *
@@ -190,4 +191,10 @@
 	return inet_ehashfn(laddr, lport, faddr, fport);
 }
 
+
+static inline int inet_iif(const struct sk_buff *skb)
+{
+	return ((struct rtable *)skb->dst)->rt_iif;
+}
+
 #endif	/* _INET_SOCK_H */