patchpanel: ndproxy: assign public v6 addr to guest-facing ifs

Currently there is no public IPv6 address assigned on the
guest-facing interfaces (arc bridges and taps) when device is on
IPv6 network. This is causing Linux choosing a wrong src address
on packets directly originated from host to guest and drop the
returning traffic.

This patch generates an EUI-64 address based on virtual interface
MAC address upon receiving an RA, and add it to the interface.

BUG=chromium:1069985
TEST=unit;fuzz
TEST=manual(deploy on octopus and verify pinging penguin from host)

Change-Id: Id3ae953df6b3c84411461294bbc8dbd236cef901
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform2/+/2428652
Tested-by: Taoyu Li <taoyl@chromium.org>
Reviewed-by: Garrick Evans <garrick@chromium.org>
Reviewed-by: Hugo Benichi <hugobenichi@google.com>
Commit-Queue: Taoyu Li <taoyl@chromium.org>
diff --git a/patchpanel/ndproxy_fuzzer.cc b/patchpanel/ndproxy_fuzzer.cc
index bef644b..002af7b 100644
--- a/patchpanel/ndproxy_fuzzer.cc
+++ b/patchpanel/ndproxy_fuzzer.cc
@@ -19,6 +19,11 @@
   NDProxy ndproxy;
   ndproxy.Init();
   ndproxy.TranslateNDFrame(data, size, guest_if_mac, out_buffer);
+  const nd_opt_prefix_info* prefix_info =
+      NDProxy::GetPrefixInfoOption(out_buffer, size);
+  // Just to consume GetPrefixInfoOption() output
+  if (prefix_info != nullptr)
+    out_buffer_extended[0] = prefix_info->nd_opt_pi_prefix_len;
   delete[] out_buffer_extended;
 
   return 0;