shill: Signal CellularService state change on registration state change

Give the manager an opportunity to connect cellular services after
activation by signalling when registration state changes.  This allows
us to correctly autoconnect cellular services after activation.

TEST=Unit tests pass; activation flows exercising this logic succeed.
BUG=chromium:162664

Change-Id: I527784b797f75523f23a7248b7c02c4002b700de
Reviewed-on: https://gerrit.chromium.org/gerrit/39030
Tested-by: Christopher Wiley <wiley@chromium.org>
Reviewed-by: Thieu Le <thieule@chromium.org>
Reviewed-by: Darin Petkov <petkov@chromium.org>
Commit-Ready: Christopher Wiley <wiley@chromium.org>
diff --git a/cellular.cc b/cellular.cc
index 80a15b5..5290236 100644
--- a/cellular.cc
+++ b/cellular.cc
@@ -375,6 +375,7 @@
     OnConnected();
   service_->SetNetworkTechnology(capability_->GetNetworkTechnologyString());
   service_->SetRoamingState(capability_->GetRoamingStateString());
+  manager()->UpdateService(service_);
 }
 
 void Cellular::HandleNewSignalQuality(uint32 strength) {