aos/sctp: Add client partial delivery stats

Change-Id: I40f8ab11cde88760215227e339715297e99e2d9f
diff --git a/aos/network/message_bridge_client.fbs b/aos/network/message_bridge_client.fbs
index 7056506..6efe3a9 100644
--- a/aos/network/message_bridge_client.fbs
+++ b/aos/network/message_bridge_client.fbs
@@ -21,6 +21,10 @@
   // Number of duplicate packets we received and dropped.
   duplicate_packets:uint (id: 4);
 
+  // Number of extra calls needed to receive a single message
+  // (indicates congestion)
+  partial_deliveries:uint (id: 5);
+
   // TODO(austin): Per channel counts?
 }