shill: On Service::Connect, connect the modem device to the network.

Also, uncouple the DBusProperties signal callbacks from Modem to make the proxy
implementation more consistent with the other proxies.

BUG=chromium-os:18727
TEST=unit tests

Change-Id: Icdddea8d2a30803150f2a159fdc5a719e960f95d
Reviewed-on: http://gerrit.chromium.org/gerrit/5444
Tested-by: Darin Petkov <petkov@chromium.org>
Reviewed-by: Chris Masone <cmasone@chromium.org>
diff --git a/modem_simple_proxy.h b/modem_simple_proxy.h
index 91fccd2..9d62ead 100644
--- a/modem_simple_proxy.h
+++ b/modem_simple_proxy.h
@@ -22,6 +22,7 @@
 
   // Inherited from ModemSimpleProxyInterface.
   virtual DBusPropertiesMap GetStatus();
+  virtual void Connect(const DBusPropertiesMap &properties);
 
  private:
   class Proxy : public org::freedesktop::ModemManager::Modem::Simple_proxy,