Fixes parameter order

pydtn/routers/base.py

@@ -11,8 +11,9 @@ class Router:
     def __call__(self, packet):
         raise NotImplementedError
 
-    def on_send_success(self, packet, target):
+    def on_send_success(self, target, packet):
         pass
 
-    def on_send_failure(self, packet, target):
+    def on_send_failure(self, target, packet):
         pass
+