We now keep the VPN enable state, bandwidth limit enable and actual limits
in the core config to avoid having to recover "user intent" from different
config files when the used VPN packages change.
Fixes#1736
The generic upgrade script is moved to run after the more specific scripts.
In addition, the script will now remove the configuration sections of
uninstalled VPN packages, so both positive and negative changes of the
default enable state can be migrated correctly.
Based-on-patch-by: Cyrus Fox <cyrus@lambdacore.de>
Fixes: #1187
