Fix single vpn-server conn issue

This commit fixes the issue where only one client was able to connect to the server.

The cause of it was the PlatformSpecificParams in water.Config that only created one tunnel utun4.

We fix it by removing it.

internal/vpn/tun_device_unix.go

@@ -12,9 +12,6 @@ import (
 func newTUNDevice() (TUNDevice, error) {
 	tun, err := water.New(water.Config{
 		DeviceType: water.TUN,
-		PlatformSpecificParams: water.PlatformSpecificParams{
-			Name: "utun4",
-		},
 	})
 	if err != nil {
 		return nil, fmt.Errorf("error allocating TUN interface: %w", err)