chmod if possible

src/freedombone-utils-firewall

@@ -38,7 +38,9 @@ function save_firewall_settings {
     printf '#!/bin/sh\n' > /etc/network/if-up.d/iptables
     printf 'iptables-restore < /etc/firewall.conf\n' >> /etc/network/if-up.d/iptables
     printf 'ip6tables-restore < /etc/firewall6.conf\n' >> /etc/network/if-up.d/iptables
-    chmod +x /etc/network/if-up.d/iptables
+    if [ -f /etc/network/if-up.d/iptables ]; then
+        chmod +x /etc/network/if-up.d/iptables
+    fi
 }
 
 function global_rate_limit {