dns/ddclient/dyndns2: fix the ovh-dyndns as reported in opnsense#3679

[interj]

This commit fixes the update process for ovh-dyndns - part of the #3679

[fichtner]

tainting dyndns2.py more or less moves us back to the whole legacy discussion around why os-dyndns had to go. It's the start of an unmaintainable mess. This parameter request should be passed by ddclient.json and generically processed by dyndns2.py

@AdSchellevis may help or take this over

[AdSchellevis]

move it into the existing definition (req_opts) unconditional and refer to https://help.dyn.com/remote-access-api/perform-update/ in the commit?

[interj]

Seeing how finicky dyndns is I would be afraid of adding it unconditionally - what if some provider will get tripped just by a presence of system parameter, regardless of its value? Would be better to add and assign system if it's configured in the UI, but I didn't look into it so much.

[AdSchellevis]

According to the specs, it doesn't do anything. we can try to add it, see if it causes issues and revert when needed. If some provider needs something special, it's also possible to provide it with its own type. When flavors of "dyndns2" exist it would also be possible to split the current implementation so there's room for modifications.

[fichtner]

Merged, thanks!