For most protocols, the operations to manage profiles require a unique
'profile-id' as index. This applies to AT, QMI and generic MBIM.
But for MBIM using the Microsoft Extensions for profile management,
this is no longer true; the device expects the 'apn-type' to be the
index.
This new property lets the user know which is the expected index field
in the Delete() and Set() operations.
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