fix(Contract): fix fiber_linked df to send to OTRS in change tariff

CHANGELOG:

### Fix
- [#963](https://git.coopdevs.org/coopdevs/som-connexio/odoo-somconnexio/-/merge_requests/963) 
Fix the DF sent to OTRS in change of tariff when break a pack contract.

Related card: https://trello.com/c/eKfYKgBC/1432-proc%C3%A9s-finalitzaci%C3%B3-contracte-ba

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