Update OpenWRT instructions

[sgryphon]

For the latest version, OpenWRT 22.03, it didn't list the iptables version of jool packages, but only netfilter ones. (i.e. opkg find '*jool*'). This means different packages need to be used. The netfilter ones were easy to set up (can be done entirely from LuCI).

So, the documentation page needs to be updated:
https://www.jool.mx/en/openwrt.html

(I think old documentation is compiled with old versions, so there could be a reference for v21 like there is for v19)

Anyway, what I did / suggested update is below:

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NAT64

For latest version, OpenWRT 22.03.

From LuCI web console:

1. System > Software: Install jool-tools-netfilter (this will install kmod-jool-netfilter and other dependencies).
2. System > Startup > Local Startup: Add the following to /etc/rc.local:

jool instance add --pool6 64:ff9b::/96

3. System > Reboot > Perform reboot
4. Confirm working NAT64 from a device inside your LAN ping 64:ff9b::8.8.8.8

Command line:

# Install packages
opkg update
opkg install kmod-jool-netfilter jool-tools-netfilter

# Add the following line to /etc/rc.local (before the exit 0)
jool instance add --pool6 64:ff9b::/96

# Confirm working NAT64 from a device inside your LAN
ping 64:ff9b::8.8.8.8

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[ydahhrk]

The pull request was merged; closing.

Thank you very much.