cromo: Expose DBus method to set network registration preference.

The Gobi modem attempts to register with CDMA 1x RTT first before trying
EVDO.  If CDMA 1x RTT is not available, it will hang the registration
process.  Since the call box can only emulate one technology, this
method can be used to force the modem to go directly to EVDO.

BUG=chromium-os:36951
TEST=cellular_Smoke (--technology=EVDO)

Change-Id: I62ff1e1d969961b79680250d3a41ca1902df409f
Reviewed-on: https://gerrit.chromium.org/gerrit/39274
Reviewed-by: Arman Uguray <armansito@chromium.org>
Reviewed-by: Ben Chan <benchan@chromium.org>
Commit-Ready: Thieu Le <thieule@chromium.org>
Tested-by: Thieu Le <thieule@chromium.org>
4 files changed