Contacts synchronization with Android removes the business role field

With Android device, if you enter a value in the role field of a contact, synchronizing with CardDAV the address book is removed.

Steps to reproduce:

• configure a DAV account on Android (with OpenSync)
• activate the synchronization of a phonebook
• create a new contact on the device for this section
• add a value in the "Role" field
• force CardDAV synchronization

Expected behaviour:

• both on the device and on the web interface the role field contains the value entered on the device before synchronization

Actual behaviour:

• both on the device and on the web interface the value entered in the role field has disappeared

Internal Ref: #64188 (thanks to Alessandro Tamberi)