Specify the AP and radio that will change power at next
calibration cycle.
0 is returned when getting the value of this node.
This node can be configured only when the mode of transmit power
control is user-triggered.
When configuring, the higher 24 bits stand for the AP index,
and the last 8 bits stand for the radio index.
4294967295 stand for configuring each radio on all APs.