wintun: migrate to wintun.dll API

Rather than having every application using Wintun driver reinvent the
wheel, the Wintun device/adapter/interface management has been moved
from wireguard-go to wintun.dll deployed with Wintun itself.

Signed-off-by: Simon Rozman <simon@rozman.si>

tun/wintun/ring_windows.go

@@ -103,8 +103,8 @@ func (descriptor *RingDescriptor) Close() {
 	}
 }
 
-func (wintun *Interface) Register(descriptor *RingDescriptor) (windows.Handle, error) {
-	handle, err := wintun.handle()
+func (wintun *Adapter) Register(descriptor *RingDescriptor) (windows.Handle, error) {
+	handle, err := wintun.OpenAdapterDeviceObject()
 	if err != nil {
 		return 0, err
 	}