HTCQualcommRIL: allow skipping of initial radio power off message

HTC 8960 radio starts by powering itself off, which leads to a race
situation where the radio powers on, then reads the power off message,
powering itself off again. Allow the initial power off
to be skipped.

Change-Id: Iebd53b98e63c8f2ec9461c7f220fa1bb7ccd1e17