shill: cellular: Support Device.SetCarrier to allow UI-based CDMA/UMTS switch.

BUG=chromium-os:32472
TEST=Unit tests. Tested on device through 'dbus-send --system --print-reply
--dest=org.chromium.flimflam /device/wwan0
org.chromium.flimflam.Device.SetCarrier "string:Generic UMTS"' -- used Foo and
'Verizon Wireless' for the carrier too -- observed updated firmware through
'modem status' and logs, or Failure in case of Foo.

Change-Id: I330f916b6116a9ec9438f600d263c546a2b561ef
Reviewed-on: https://gerrit.chromium.org/gerrit/32389
Tested-by: Darin Petkov <petkov@chromium.org>
Reviewed-by: Ben Chan <benchan@chromium.org>
Commit-Ready: Darin Petkov <petkov@chromium.org>
diff --git a/device.cc b/device.cc
index 6086045..910abf9 100644
--- a/device.cc
+++ b/device.cc
@@ -216,6 +216,13 @@
                         "Device doesn't support ChangePIN.");
 }
 
+void Device::SetCarrier(const string &/*carrier*/,
+                        Error *error, const ResultCallback &/*callback*/) {
+  SLOG(Device, 2) << __func__;
+  Error::PopulateAndLog(error, Error::kNotSupported,
+                        "Device doesn't support SetCarrier.");
+}
+
 void Device::DisableIPv6() {
   SetIPFlag(IPAddress::kFamilyIPv6, kIPFlagDisableIPv6, "1");
 }