int sixrd_add_tunnel (ip6_address_t * ip6_prefix, u8 ip6_prefix_len,
ip4_address_t * ip4_prefix, u8 ip4_prefix_len,
ip4_address_t * ip4_src, bool security_check,
int sixrd_add_tunnel (ip6_address_t * ip6_prefix, u8 ip6_prefix_len,
ip4_address_t * ip4_prefix, u8 ip4_prefix_len,
ip4_address_t * ip4_src, bool security_check,