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/linux/Kbuild b/include/linux/Kbuild
index e2ea0b2..2fc8e14 100644
--- a/include/linux/Kbuild
+++ b/include/linux/Kbuild
@@ -94,6 +94,7 @@
 header-y += if_slip.h
 header-y += if_strip.h
 header-y += if_tun.h
+header-y += if_x25.h
 header-y += in_route.h
 header-y += ioctl.h
 header-y += ip6_tunnel.h