shill: cellular: make enable and disable for universal modems

Make enable and disable for universal modems.

BUG=chromium-os:28700
TEST=run unit tests, enable and disable a Y3300

Change-Id: Icaaa72b976bed0f597dac2c46140172a8d901913
Reviewed-on: https://gerrit.chromium.org/gerrit/19913
Commit-Ready: Jason Glasgow <jglasgow@chromium.org>
Reviewed-by: Jason Glasgow <jglasgow@chromium.org>
Tested-by: Jason Glasgow <jglasgow@chromium.org>
diff --git a/cellular.h b/cellular.h
index 472fa48..1a2375b 100644
--- a/cellular.h
+++ b/cellular.h
@@ -186,6 +186,7 @@
   friend class CellularCapabilityTest;
   friend class CellularCapabilityCDMATest;
   friend class CellularCapabilityGSMTest;
+  friend class CellularCapabilityUniversalTest;
   friend class CellularServiceTest;
   friend class ModemTest;
   FRIEND_TEST(CellularCapabilityCDMATest, CreateFriendlyServiceName);