Update the docstring on getAllCellInfo() for unreported values

In the event that not all fields are available for a particular
cell information report, those values are set to
Integer.MAX_VALUE. In addition, this docstring clarifies the
minimum expectation for what will be reported in all cases.

Bug: 32364031
Test: none
Change-Id: Ic5df72f69e5917eb495d349a380ced53a80408fa