First set of code review patches

src/tun_linux.go

@@ -7,6 +7,7 @@ import (
 	"encoding/binary"
 	"errors"
 	"golang.org/x/sys/unix"
+	"net"
 	"os"
 	"strings"
 	"unsafe"
@@ -19,6 +20,11 @@ type NativeTun struct {
 	name string
 }
 
+func (tun *NativeTun) IsUp() (bool, error) {
+	inter, err := net.InterfaceByName(tun.name)
+	return inter.Flags&net.FlagUp != 0, err
+}
+
 func (tun *NativeTun) Name() string {
 	return tun.name
 }