ufw init script dependencies

With the standard dependencies, ufw will not properly start up, example:

* Starting ufw …
Another app is currently holding the xtables lock. Perhaps you want to use the -w option?
ip6tables-restore: line 2 failed
Problem running ‘/etc/ufw/before6.rules’
* Failed to start ufw.
* ERROR: ufw failed to start

It is necessary to add dependencies to ip(6)tables like so:

depend() {
	before net
	after iptables ip6tables # these need to be added
	provide firewall
}