[rilmodem]preferred RAT mode value mapping for new UI design

UI labels will change from '3G' to 'Prefer 3G'. Ofono-RIL constant values
need to be update accordingly

Signed-off-by: Petri Takalokastari <petri.takalokastari@oss.tieto.com>
Merge pull request #60 from ptakalok/master

[rilmodem]preferred RAT mode value mapping for new UI design