IP6_GRE_HASH_SIZE
#define HASH_KEY(key) (((__force u32)key^((__force u32)key>>4))&(IP6_GRE_HASH_SIZE - 1))
for (h = 0; h < IP6_GRE_HASH_SIZE; h++) {
struct ip6_tnl __rcu *tunnels[4][IP6_GRE_HASH_SIZE];