Mwan3 from 19.07 to 21.02

[fma]

Within recent weeks I did upgrade from 19.07-8 to 21.02-8. Platform x86, current application packages. Interfaces WAN, WWAN, tun with openvpn, lately also a wireguard interfaces
Finally, I got it running again. Just some findings/workaround I would like to address. Maybe somebody has a hint on one of them.

1. All my rules had to be set explicitly to 'IPv4 only'. Probably a typical RTFM, but this was an initially pitfall due to source based rules.
2. To make it work, I have to apply the commands for the default routes in all device specific routing tables following 'wan' (table 1) within /etc/mwan3.user
3. Even all is finally running fine, mwan3 interfaces, lets me know: 'interface wan is error (4) and tracking is active' for the
   working interfaces.
4. On 21.02-1, there is a mwan3track process for every interface that is not explicitly disabled. 19.07-8 had only such processes for actually active devices

[fma]

5. adblock:
   19.07-8 --> /usr/bin/sort -> 'kind of gnusort' (ok)
   21.02-1 --> /usr/bin/sort -> ../../bin/busybox (fails)
   !!! even a sort from coreutils is installed
   Fix: rm sort ; ln -s ../../libexec/sort-coreutils sort

[fma]

Solution for 3: Looks like, nobody else has the issue. Then it must be easy ...
Suspected package 'ip-tiny' and removed it ... then discovered

1. ip-tiny is just the link to busybox, while ip-full links to the full gnu-tool. However, ip-full is installed and ip-tiny whether installed or not is 'almost' no impact, but ...
2. Removing 'ip-tiny' also removed the 'mwan3' and 'luci-mwan3...' packages.
   After re-installing the mwan3-packages ... issue resolved: 'mwan3 interfaces' returns reasonable output, again. Nice!

However, default routes for tun and wireguard specific tables still need to be added by /etc/mwan3.user (my 2nd point)
If is meant to be configured in luci, then it keeps hiding from me.
But finally, I can live pretty well with the way it is now.

Solution for 4.: If a user decides to keep unused interfaces in the config, then setting the unused interfaces to 'Not enabled' and 'Offline' will omit the unwanted mwan3track processes.

Finally, another nice thing in 21.02-1: Restarting mwan3 from the shell
'service mwan3 restart'
does less endless unwanted output to send to /dev/null, now. And even better: The output actually stops after the messages about already existing routes for certain interfaces. Even nicer!