ipv6: sr: add missing Kbuild export for header files

Add missing IPv6-SR header files in include/uapi/linux/Kbuild.

Also, prevent seg6_lwt_headroom() from being exported and add
missing linux/types.h include.

Signed-off-by: David Lebrun <david.lebrun@uclouvain.be>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/uapi/linux/seg6.h b/include/uapi/linux/seg6.h
index c396a80..3349659 100644
--- a/include/uapi/linux/seg6.h
+++ b/include/uapi/linux/seg6.h
@@ -14,6 +14,8 @@
 #ifndef _UAPI_LINUX_SEG6_H
 #define _UAPI_LINUX_SEG6_H
 
+#include <linux/types.h>
+
 /*
  * SRH
  */