Fixed incorrect RAT set in PS WWAN registration info

RAT ratcheter uses ServiceState.getRilDataRadioTechnology which
can get data RAT IWLAN when the device is camped on IWLAN. Then
it set IWLAN as the RAT in PS WWAN registration info.

Fixed by directly using the RAT from network registration info
instead of using the one in ServiceState, which might return
RAT from PS WLAN in some cases.

Bug: 130820694
Test: Manual + unit tests
Change-Id: I1a1f9dd692a6920dfbe5177a9098643d2c24913a