Using default in ALT distributins 'ip' utils instead of ifconfig one.

--- ./src/device-linux.C
+++ ./src/device-linux.C
@@ -70,7 +70,7 @@ tap_device::info ()
 const char *
 tap_device::if_up ()
 {
-  return "/sbin/ifconfig $IFNAME hw ether $MAC mtu $MTU";
+  return "/sbin/ip link set $IFNAME up address $MAC mtu $MTU";
 }
 
 tap_device::tap_device ()