ipv6: ip6_gre: Replace rcu_assign_pointer() with RCU_INIT_POINTER()

According to RCU_INIT_POINTER()'s block comment 3.a, it can be used if
"3. The referenced data structure has already been exposed to readers either
at compile time or via rcu_assign_pointer() -and-
a. You have not made -any- reader-visible changes to this structure since
then".

This case fulfills the conditions above because between the rtnl_dereference() call and the rcu_assign_pointer() call there is no update of that value. Therefore, this patch makes the replacement.

The following Coccinelle semantic patch was used:
@@
@@

- rcu_assign_pointer
+ RCU_INIT_POINTER
(...,
(
rtnl_dereference(...)
|
rcu_dereference_protected(...)
) )

---
 net/ipv6/ip6_gre.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index 3873181..67dcaca 100644
@@ -261,7 +261,7 @@ static void ip6gre_tunnel_link(struct ip6gre_net *ign, struct ip6_tnl *t)
 {
 	struct ip6_tnl __rcu **tp = ip6gre_bucket(ign, t);
 
-	rcu_assign_pointer(t->next, rtnl_dereference(*tp));
+	RCU_INIT_POINTER(t->next, rtnl_dereference(*tp));
 	rcu_assign_pointer(*tp, t);
 }
 

1.9.1