Update documentation to clarify RIL_REQUEST_GET_ACTIVITY_INFO
Nathan Harold authored
The documentation for RIL_REQUEST_GET_ACTIVITY_INFO allowed for
critically disruptive behavior in the implementation of the API.
This is a documentation update to ensure that there will be
exactly one power state reported in each millisecond, which
is important for proper power accounting in FDD.

Bug: 32061813
Test: none
Change-Id: I2835d5ad298eaa8cfea2e1a90342f290183f698d
c8635211