[shill] Wire up derived properties in the Device class

BUG=chromium-os:16343
TEST=unit tests

Change-Id: Ib35efbc00133b6ffc9352e52c0413be4bd984e12
Reviewed-on: http://gerrit.chromium.org/gerrit/3559
Tested-by: Chris Masone <cmasone@chromium.org>
Reviewed-by: mukesh agrawal <quiche@chromium.org>
diff --git a/ipconfig.cc b/ipconfig.cc
index 339a198..a1d4182 100644
--- a/ipconfig.cc
+++ b/ipconfig.cc
@@ -20,6 +20,10 @@
   VLOG(2) << __func__ << " device: " << device_name();
 }
 
+string IPConfig::GetRpcIdentifier() {
+  return adaptor_->GetRpcIdentifier();
+}
+
 bool IPConfig::RequestIP() {
   return false;
 }