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/routing/ip.go

@@ -19,8 +19,8 @@ var (
 )
 
 func ipMatchesFamily(ip netip.Addr, family int) bool {
-	return (family == netlink.FAMILY_V4 && ip.Is4()) ||
-		(family == netlink.FAMILY_V6 && ip.Is6())
+	return (family == netlink.FamilyV4 && ip.Is4()) ||
+		(family == netlink.FamilyV6 && ip.Is6())
 }
 
 func (r *Routing) assignedIP(interfaceName string, family int) (ip netip.Addr, err error) {