Fix docstrings for RIL_CellIdentity

Fix docstrings for RIL_CellIdentity

Update the documentation to match the current
CTS requirements for Cell Identity reporting
-For LTE, WCDMA, and GSM require that the channel
 number be reported.
-For LTE and WCDMA, require that the correct
 physical channel identifier be reported. Note that
 due to b/32774471 we still cannot require BSIC
 to be reported.

Bug: 65174915
Test: none, comment-only change
Change-Id: I6866e3e78678aeb2b8f48bff032709f802cba067
Merged-In: I6866e3e78678aeb2b8f48bff032709f802cba067
(cherry picked from commit ae339b3feb9d10c24a35db9c6ad01df5deeab1e0)