ClatdController - disable IPv6 on clatd tun interface

Test: we *continue* to not get clatd complaints about unknown packets
  even with a revert in clatd to ignore them
Bug: 129305844
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: If6961a9856cfd3b9a041eb155688b5a18d2b5223