Try to make the tun replacable

Former-commit-id: 6be0958887

device/tun_unix.go

@@ -5,6 +5,7 @@ package device
 import (
 	"net"
 	"os"
+	"runtime"
 
 	"github.com/fosrl/newt/logger"
 	"golang.org/x/sys/unix"
@@ -13,6 +14,11 @@ import (
 )
 
 func CreateTUNFromFD(tunFd uint32, mtuInt int) (tun.Device, error) {
+	if runtime.GOOS == "android" { // otherwise we get a permission denied
+		theTun, _, err := tun.CreateUnmonitoredTUNFromFD(int(tunFd))
+		return theTun, err
+	} 
+	
 	dupTunFd, err := unix.Dup(int(tunFd))
 	if err != nil {
 		logger.Error("Unable to dup tun fd: %v", err)