Assign name to router4G new contract when changing holders

CHANGELOG:

### Fixed
- [#734](https://gitlab.com/coopdevs/odoo-somconnexio/-/merge_requests/734) Assign name to router4G new contract when changing holders

Related card: https://trello.com/c/IrmTE5au/1150-no-podem-fer-canvis-de-titular-per-router-4g

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We solve the error when changing holders