There are multiple issues in IPv6 userspace tunnel
implementation. Even the kernel module that ships with
2.5 does not support IPv6 tunneling. There is not
enough time to get all fixes in branch-2.5. So it make
sense to disable the support on 2.5.
Signed-off-by: Pravin B Shelar <pshelar@ovn.org> Acked-by: Flavio Leitner <fbl@sysclose.org> Acked-by: Thadeu Lima de Souza Cascardo <cascardo@redhat.com> Acked-by: Jesse Gross <jesse@kernel.org>