Add forground flag to carrierservice binder.

The persistent carrier binding is made with only the BIND_AUTO_CREATE flag, not the BIND_FOREGROUND_SERVICE flag. Without this flag, the binding alone is not enough to keep the application from being restricted in various power saving modes, which is a major purpose of the binding.

Bug: b/27853835
Change-Id: I03c36e886fb03d8a410913eaf4bffa38c12a4499