[client] Refactor/iface pkg (#2646)

Refactor the flat code structure

client/iface/iface_create.go

@@ -0,0 +1,19 @@
+//go:build (!android && !darwin) || ios
+
+package iface
+
+// Create creates a new Wireguard interface, sets a given IP and brings it up.
+// Will reuse an existing one.
+// this function is different on Android
+func (w *WGIface) Create() error {
+	w.mu.Lock()
+	defer w.mu.Unlock()
+
+	cfgr, err := w.tun.Create()
+	if err != nil {
+		return err
+	}
+
+	w.configurer = cfgr
+	return nil
+}