shill: vpn: Associate VPN device with service and update IP configuration.

BUG=chromium-os:27384,chromium-os:27385
TEST=unit tests

Change-Id: I5b35bebeadd25f50f7044d2e4ec5bc121a56835e
Reviewed-on: https://gerrit.chromium.org/gerrit/17488
Commit-Ready: Darin Petkov <petkov@chromium.org>
Reviewed-by: Darin Petkov <petkov@chromium.org>
Tested-by: Darin Petkov <petkov@chromium.org>
diff --git a/ipconfig.h b/ipconfig.h
index b3afed2..e86ea57 100644
--- a/ipconfig.h
+++ b/ipconfig.h
@@ -75,6 +75,7 @@
   void RegisterUpdateCallback(
       Callback2<const IPConfigRefPtr&, bool>::Type *callback);
 
+  void set_properties(const Properties &props) { properties_ = props; }
   const Properties &properties() const { return properties_; }
 
   // Request, renew and release IP configuration. Return true on success, false