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.cc b/modem_simple_proxy.cc
index a8b48b1..37c9c83 100644
--- a/modem_simple_proxy.cc
+++ b/modem_simple_proxy.cc
@@ -19,6 +19,10 @@
   return proxy_.GetStatus();
 }
 
+void ModemSimpleProxy::Connect(const DBusPropertiesMap &properties) {
+  proxy_.Connect(properties);
+}
+
 ModemSimpleProxy::Proxy::Proxy(DBus::Connection *connection,
                                const string &path,
                                const string &service)