chore(netlink): define own types with minimal fields

- Allow to swap `github.com/vishvananda/netlink`
- Allow to add build tags for each platform
- One step closer to development on non-Linux platforms

internal/wireguard/route.go

@@ -2,17 +2,17 @@ package wireguard
 
 import (
 	"fmt"
-	"net"
+	"net/netip"
 
 	"github.com/qdm12/gluetun/internal/netlink"
 )
 
 // TODO add IPv6 route if IPv6 is supported
 
-func (w *Wireguard) addRoute(link netlink.Link, dst *net.IPNet,
+func (w *Wireguard) addRoute(link netlink.Link, dst netip.Prefix,
 	firewallMark int) (err error) {
-	route := &netlink.Route{
-		LinkIndex: link.Attrs().Index,
+	route := netlink.Route{
+		LinkIndex: link.Index,
 		Dst:       dst,
 		Table:     firewallMark,
 	}
@@ -21,7 +21,7 @@ func (w *Wireguard) addRoute(link netlink.Link, dst *net.IPNet,
 	if err != nil {
 		return fmt.Errorf(
 			"adding route for link %s, destination %s and table %d: %w",
-			link.Attrs().Name, dst, firewallMark, err)
+			link.Name, dst, firewallMark, err)
 	}
 
 	return err