MEDIUM: quic: Make sure we return the tasklet from qcc_io_cb

In qcc_io_cb, return the tasklet to tell the scheduler the tasklet is
still alive, it is not yet needed, but will be soon.

src/mux_quic.c

@@ -3217,7 +3217,7 @@ struct task *qcc_io_cb(struct task *t, void *ctx, unsigned int status)
 
 	TRACE_LEAVE(QMUX_EV_QCC_WAKE, qcc->conn);
 
-	return NULL;
+	return t;
 
  release:
 	qcc_shutdown(qcc);