firewall: don't reload if there were no address or data changes

This fixes packet loss due to reloading firewall every minute with IPv6
implementation of certain ISPs.

SVN-Revision: 39332

package/network/config/firewall/files/firewall.hotplug

@@ -1,6 +1,7 @@
 #!/bin/sh
 
 [ "$ACTION" = ifup -o "$ACTION" = ifupdate ] || exit 0
+[ "$ACTION" = ifupdate -a -z "$IFUPDATE_ADDRESSES" -a -z "$IFUPDATE_DATA" ] && exit 0
 
 /etc/init.d/firewall enabled || exit 0