SPINEL_PROP_THREAD_MGMT_GET_ACTIVE_DATASET value

Send MGMT_GET Thread Active Operational Dataset Format: `A(t(iD))` - Write only The formatting of this property follows the same rules as in SPINEL_PROP_THREAD_MGMT_SET_ACTIVE_DATASET. This property further allows the sender to not include a value associated with properties in formatting of `t(iD)`, i.e., it should accept either a `t(iD)` or a `t(i)` encoding (in both cases indicating that the associated Dataset property should be requested as part of MGMT_GET command). This is write-only property. When written, it triggers a MGMT_ACTIVE_GET meshcop command to be sent to leader requesting the Dataset related properties from the format. The spinel frame response should be a `LAST_STATUS` with the status of the transmission of MGMT_ACTIVE_GET command. In addition to supported properties in SPINEL_PROP_THREAD_MGMT_SET_ACTIVE_DATASET, the following property can be optionally included in the Dataset: SPINEL_PROP_DATASET_DEST_ADDRESS