Warn on out-of-order or duplicated packets (or missing nonce increment!)

src/network/network.h

@@ -102,11 +102,14 @@ namespace Network {
     double SRTT;
     double RTTVAR;
 
-    /* Exception from send(), to be delivered if the frontend asks for it,
+    /* Exception from send() or recv(), to be delivered if the frontend asks for it,
        without altering control flow. */
     bool have_send_exception;
     NetworkException send_exception;
 
+    bool have_recv_exception;
+    NetworkException recv_exception;
+
     Packet new_packet( string &s_payload );
 
   public:
@@ -132,6 +135,11 @@ namespace Network {
     {
       return have_send_exception ? &send_exception : NULL;
     }
+
+    const NetworkException *get_recv_exception( void ) const
+    {
+      return have_recv_exception ? &recv_exception : NULL;
+    }
   };
 }