vti6: fix device register to report IFLA_INFO_KIND

vti6 interface is registered before the rtnl_link_ops block
is attached. As a result the resulting RTM_NEWLINK is missing
IFLA_INFO_KIND. Re-order attachment of rtnl_link_ops block to fix.

Signed-off-by: Dave Forster <dforster@brocade.com>
Signed-off-by: David S. Miller <davem@davemloft.net>