bind: Fix ipv6 detection logic

Bug was introduced in a7b770eec4 and
results in bind always stating with the `-4` flag.

Signed-off-by: Rucke Teg <rucketeg@protonmail.com>

net/bind/files/named.init

@@ -73,7 +73,7 @@ start_service() {
     touch $conf_local_file
 
     local args=
-    [ no_ipv6 ] && args="-4"
+    no_ipv6 && args="-4"
 
     procd_open_instance
     procd_set_param command /usr/sbin/named -u bind -f $args -c $config_file