Update to kernel headers v4.12.3.

Test: Built angler.
Change-Id: Icbcf4fac2334de8409b049ed7a3b4c24b4e98ce9
diff --git a/libc/kernel/uapi/linux/nbd.h b/libc/kernel/uapi/linux/nbd.h
index e8fc47c..50079fa 100644
--- a/libc/kernel/uapi/linux/nbd.h
+++ b/libc/kernel/uapi/linux/nbd.h
@@ -42,6 +42,7 @@
 #define NBD_FLAG_SEND_FLUSH (1 << 2)
 #define NBD_FLAG_SEND_TRIM (1 << 5)
 #define NBD_FLAG_CAN_MULTI_CONN (1 << 8)
+#define NBD_CFLAG_DESTROY_ON_DISCONNECT (1 << 0)
 #define NBD_REQUEST_MAGIC 0x25609513
 #define NBD_REPLY_MAGIC 0x67446698
 struct nbd_request {