Update to kernel headers v4.12.3.

Test: Built angler.
Change-Id: Icbcf4fac2334de8409b049ed7a3b4c24b4e98ce9
diff --git a/libc/kernel/uapi/linux/if.h b/libc/kernel/uapi/linux/if.h
index 15207e2..d815ef8 100644
--- a/libc/kernel/uapi/linux/if.h
+++ b/libc/kernel/uapi/linux/if.h
@@ -22,6 +22,7 @@
 #include <linux/types.h>
 #include <linux/socket.h>
 #include <linux/compiler.h>
+#include <sys/socket.h>
 #if __UAPI_DEF_IF_IFNAMSIZ
 #define IFNAMSIZ 16
 #endif