Add comments to GSM and CDMA getDbm()

Bug: 148912739
Test: make
Change-Id: I9be4caeda8f50645bc742e95bfd7ba067a02883f
Merged-In: I9be4caeda8f50645bc742e95bfd7ba067a02883f
(cherry picked from commit b78e84c5226afdf94bc0ba0119d65b926cb37d1d)
2 files changed