Update to v6.4 kernel headers.

Kernel headers coming from:

Git: https://android.googlesource.com/kernel/common/
Branch: android-mainline
Tag: android-mainline-6.4

Test: Bionic unit tests pass.
Change-Id: I991f8eaa2b272a464166addb13e6bdc63734444d
diff --git a/libc/kernel/uapi/linux/ipv6.h b/libc/kernel/uapi/linux/ipv6.h
index d62d269..d8fe3cd 100644
--- a/libc/kernel/uapi/linux/ipv6.h
+++ b/libc/kernel/uapi/linux/ipv6.h
@@ -62,7 +62,7 @@
 struct rt0_hdr {
   struct ipv6_rt_hdr rt_hdr;
   __u32 reserved;
-  struct in6_addr addr[0];
+  struct in6_addr addr[];
 #define rt0_type rt_hdr.type
 };
 struct rt2_hdr {