Remove Attachement(or Assignation Level) to Attribute Model

[sbernard31]

An attribute is fully determined by several characteristics.

LWM2M v1.1.1 defines :

Attribute characteristic	Description
Attachment	The Object, Object Instance, or Resource, to which an Attribute is logically applied
Assignation Level	The Level (Object, Object Instance, Resource, Resource Instance) where the value of the Attribute is set (by WRITE-ATTRIBUTES).

(source : LWM2M-v1.1.1@core§Table: 5.1.1.-1 Attribute Characteristics)

But in LWM2M v1.2.1, Asignation Level was removed from Attribute characteristic.	Attribute characteristic	Description
Attachment	The Level (Object, Object Instance, Resource, Resource Instance) to which an Attribute is attached

(Source : LWM2M-v1.2.1@core§Table: 7.3.-1 Attribute Characteristics)

The reason seems to be that it was confusing and redundant : https://github.com/OpenMobileAlliance/OMA_LwM2M_for_Developers/issues/539#issuecomment-1039159909

Currently in Leshan,

• LwM2mAttributeModel has attributes for both concept Asignation Level and Attachment
• Attachment is not really used.
• Asignation Level is used with meaning of LWM2M v1.2.1 Attachment concept.

So in Leshan, we should probably :

• remove one those concept (as only 1 is really used)
• maybe better to keep Attachment even if this is more LWM2M v1.2.1 wording (as it seems this is the fixed version of LWM2M concept)

[sbernard31]

Implemented by 6c03a3d34a138870d5051555dec8b443bb913f35 and integrated in master.

It will be available in next release (2.0.0-M15)