Simply call sum on sizes for bytes sent

Author: jakirkham

distributed/comm/ucx.py

@@ -206,7 +206,7 @@ async def write(
 
                 for each_frame in send_frames:
                     await self.ep.send(each_frame)
-                return sum(map(nbytes, send_frames))
+                return sum(sizes)
             except (ucp.exceptions.UCXBaseException):
                 self.abort()
                 raise CommClosedError("While writing, the connection was closed")