feat(dev): support development on darwin (OSX)

- Netlink linux tagged files
- Netlink linux || darwin tagged files
- Create non-implemented files for NOT linux
- Create non-implemented files for NOT linux and NOT darwin
- Specify wireguard netlink integration test as for linux only

internal/netlink/route_unspecified.go

@@ -0,0 +1,20 @@
+//go:build !linux && !darwin
+
+package netlink
+
+func (n *NetLink) RouteList(link *Link, family int) (
+	routes []Route, err error) {
+	panic("not implemented")
+}
+
+func (n *NetLink) RouteAdd(route Route) error {
+	panic("not implemented")
+}
+
+func (n *NetLink) RouteDel(route Route) error {
+	panic("not implemented")
+}
+
+func (n *NetLink) RouteReplace(route Route) error {
+	panic("not implemented")
+}