Telephony: Read signal strength values as expected

Telephony framework expects Lte rsrp and rsrq, as well
as dbm and ecio values for cdma and evdoe to be negative.
RIL Interface provides positive values.
Fix that by changing the constructor from Parcel to
also multiply by -1
Writing to parcel also modified for consistency

Bug: 10440827
Change-Id: I6a8112a5b343c5e6c6dc12332a6e9a489b093cc1