python/debuglink: properly use session_counter for debuglink transport

python/src/trezorlib/debuglink.py

@@ -281,9 +281,11 @@ class TrezorClientDebugLink(TrezorClient):
 
     def open(self):
         super().open()
+        if self.session_counter == 1:
             self.debug.open()
 
     def close(self):
+        if self.session_counter == 1:
             self.debug.close()
         super().close()