iptables: replace open-coded sizeof by ARRAY_SIZE

Signed-off-by: Jan Engelhardt <jengelh@medozas.de>
diff --git a/iptables-restore.c b/iptables-restore.c
index f1c5e3e..2a797cc 100644
--- a/iptables-restore.c
+++ b/iptables-restore.c
@@ -99,7 +99,7 @@
  * returns true if argument added, false otherwise */
 static int add_argv(char *what) {
 	DEBUGP("add_argv: %s\n", what);
-	if (what && ((newargc + 1) < sizeof(newargv)/sizeof(char *))) {
+	if (what && newargc + 1 < ARRAY_SIZE(newargv)) {
 		newargv[newargc] = strdup(what);
 		newargc++;
 		return 1;