tools/rctest: Fix file descriptor leak

Closed the file before returning from do_send function.
diff --git a/tools/rctest.c b/tools/rctest.c
index 383d165..9169e3c 100644
--- a/tools/rctest.c
+++ b/tools/rctest.c
@@ -559,6 +559,7 @@
 		}
 		len = read(fd, buf, data_size);
 		send(sk, buf, len, 0);
+		close(fd);
 		return;
 	} else {
 		for (i = 6; i < data_size; i++)