Expose stop service advertisment on Windows

[johnb8]

It seems like you need to call StopAdvertising on the GattServiceProvider when you want to change the service being advertised or else Windows will just advertise both services. This just exposes that function on the adapter but only for Windows. I added a dummy function on the Linux implementation so apps that use it still build without having to make Linux and Windows specific files.

I'm not sure if a Linux implementation is needed or if BlueZ handles this differently.