Always assume evdoXxxx signal strength values are correct.

This solves a race condition between the network type changing and
a signal strength changing. This could cause StatusBarPolicy to see
the -1 values for the evdo strength parameters and hence 0 bars would
be displayed.

Bug: 2419251
Change-Id: Iba0bdbd2023b6a5e49fc1f82c997ec3219158286