[shill] Make IPConfig objects have sane DBus Paths

following the following schema: /ipconfig/<devicename>_<per-run serial number>_<config type>

BUG=chromium-os:17744
TEST=unit, run on device and use /usr/local/lib/flimflam/list-devices

Change-Id: Ia88814d46facce525d866c8309556131d8fb6a0d
Reviewed-on: http://gerrit.chromium.org/gerrit/4535
Tested-by: Chris Masone <cmasone@chromium.org>
Reviewed-by: Darin Petkov <petkov@chromium.org>
diff --git a/dhcp_config.h b/dhcp_config.h
index 1d7256c..0ad62c4 100644
--- a/dhcp_config.h
+++ b/dhcp_config.h
@@ -79,6 +79,8 @@
   static const char kReasonReboot[];
   static const char kReasonRenew[];
 
+  static const char kType[];
+
   // Starts dhcpcd, returns true on success and false otherwise.
   bool Start();