[client] skip UAPI listener in netstack mode (#5397)

In netstack (proxy) mode, the process lacks permission to create
/var/run/wireguard, making the UAPI listener unnecessary and causing
a misleading error log. Introduce NewUSPConfigurerNoUAPI and use it
for the netstack device to avoid attempting to open the UAPI socket
entirely. Also consolidate UAPI error logging to a single call site.

client/iface/configurer/uapi.go

@@ -5,20 +5,18 @@ package configurer
 import (
 	"net"
 
-	log "github.com/sirupsen/logrus"
 	"golang.zx2c4.com/wireguard/ipc"
 )
 
 func openUAPI(deviceName string) (net.Listener, error) {
 	uapiSock, err := ipc.UAPIOpen(deviceName)
 	if err != nil {
-		log.Errorf("failed to open uapi socket: %v", err)
 		return nil, err
 	}
 
 	listener, err := ipc.UAPIListen(deviceName, uapiSock)
 	if err != nil {
-		log.Errorf("failed to listen on uapi socket: %v", err)
+		_ = uapiSock.Close()
 		return nil, err
 	}