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/link_unspecified.go

@@ -0,0 +1,31 @@
+//go:build !linux && !darwin
+
+package netlink
+
+func (n *NetLink) LinkList() (links []Link, err error) {
+	panic("not implemented")
+}
+
+func (n *NetLink) LinkByName(name string) (link Link, err error) {
+	panic("not implemented")
+}
+
+func (n *NetLink) LinkByIndex(index int) (link Link, err error) {
+	panic("not implemented")
+}
+
+func (n *NetLink) LinkAdd(link Link) (linkIndex int, err error) {
+	panic("not implemented")
+}
+
+func (n *NetLink) LinkDel(link Link) (err error) {
+	panic("not implemented")
+}
+
+func (n *NetLink) LinkSetUp(link Link) (linkIndex int, err error) {
+	panic("not implemented")
+}
+
+func (n *NetLink) LinkSetDown(link Link) (err error) {
+	panic("not implemented")
+}