iptables: close open file descriptors

Just for correctness, close some file descriptors that were opened.
(E.g. ip6tables-save reading from procfs files.)

Signed-off-by: Jan Engelhardt <jengelh@medozas.de>
diff --git a/iptables-save.c b/iptables-save.c
index 6000b49..f63ee6b 100644
--- a/iptables-save.c
+++ b/iptables-save.c
@@ -52,6 +52,7 @@
 		ret &= func(tablename);
 	}
 
+	fclose(procfile);
 	return ret;
 }