feat(internal/wireguard): opportunistic kernelspace

- Auto detect if kernelspace implementation is available
- Fallback to Go userspace implementation if kernel is not available

internal/wireguard/netlinker.go

@@ -10,9 +10,11 @@ type NetLinker interface {
 	RouteAdd(route *netlink.Route) error
 	RuleAdd(rule *netlink.Rule) error
 	RuleDel(rule *netlink.Rule) error
+	LinkAdd(link netlink.Link) (err error)
 	LinkList() (links []netlink.Link, err error)
 	LinkByName(name string) (link netlink.Link, err error)
 	LinkSetUp(link netlink.Link) error
 	LinkSetDown(link netlink.Link) error
 	LinkDel(link netlink.Link) error
+	IsWireguardSupported() (ok bool, err error)
 }