Update to kernel headers v4.12.3.

Test: Built angler.
Change-Id: Icbcf4fac2334de8409b049ed7a3b4c24b4e98ce9
diff --git a/libc/kernel/uapi/linux/seg6_iptunnel.h b/libc/kernel/uapi/linux/seg6_iptunnel.h
index fdd4705..747fa09 100644
--- a/libc/kernel/uapi/linux/seg6_iptunnel.h
+++ b/libc/kernel/uapi/linux/seg6_iptunnel.h
@@ -18,6 +18,7 @@
  ****************************************************************************/
 #ifndef _UAPI_LINUX_SEG6_IPTUNNEL_H
 #define _UAPI_LINUX_SEG6_IPTUNNEL_H
+#include <linux/seg6.h>
 enum {
   SEG6_IPTUNNEL_UNSPEC,
   SEG6_IPTUNNEL_SRH,