Update to v4.15 kernel headers.

Test: Compiles, boots bullhead/hikey960.
Change-Id: I118beb8b6cac0881b1270f9bf6981959297a41a8
diff --git a/libc/kernel/uapi/linux/if_tun.h b/libc/kernel/uapi/linux/if_tun.h
index 4912d7b..d8757a1 100644
--- a/libc/kernel/uapi/linux/if_tun.h
+++ b/libc/kernel/uapi/linux/if_tun.h
@@ -51,6 +51,8 @@
 #define TUNGETVNETBE _IOR('T', 223, int)
 #define IFF_TUN 0x0001
 #define IFF_TAP 0x0002
+#define IFF_NAPI 0x0010
+#define IFF_NAPI_FRAGS 0x0020
 #define IFF_NO_PI 0x1000
 #define IFF_ONE_QUEUE 0x2000
 #define IFF_VNET_HDR 0x4000