Resend any reliable messages received before startup

We want to be able to publish (and receive) low frequency configuration
messages.  This lets us make those *not* periodic when we move them
across nodes, simplifying the system.

This takes some special tracking at startup.  We very much don't want to
re-send messages already sent.  That would result in 2 receive
timestamps for a single node for 1 send packet, probably breaking log
sorting.  I'm not interested in learning what would break...

Change-Id: I489460cd4919907516e504e6694d7cef544b0da6
diff --git a/aos/network/message_bridge_client.fbs b/aos/network/message_bridge_client.fbs
index 9dddd16..7056506 100644
--- a/aos/network/message_bridge_client.fbs
+++ b/aos/network/message_bridge_client.fbs
@@ -18,6 +18,9 @@
   // to get their monotonic time.
   monotonic_offset:int64 (id: 3);
 
+  // Number of duplicate packets we received and dropped.
+  duplicate_packets:uint (id: 4);
+
   // TODO(austin): Per channel counts?
 }