X25: Add if_x25.h and x25 to device identifiers

V2 Feedback from John Hughes.
- Add header for userspace implementations such as xot/xoe to use
- Use explicit values for interface stability
- No changes to driver patches

V1
- Use identifiers instead of magic numbers for X25 layer 3 to device interface.
- Also fixed checkpatch notes on updated code.

[ Add new user header to include/linux/Kbuild  -DaveM ]

Signed-off-by: Andrew Hendry <andrew.hendry@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/x25device.h b/include/net/x25device.h
index 1415bcf..1fa08b4 100644
--- a/include/net/x25device.h
+++ b/include/net/x25device.h
@@ -3,6 +3,7 @@
 
 #include <linux/if_ether.h>
 #include <linux/if_packet.h>
+#include <linux/if_x25.h>
 #include <linux/skbuff.h>
 
 static inline __be16 x25_type_trans(struct sk_buff *skb, struct net_device *dev)