net,rcu: convert call_rcu(__nf_ct_ext_free_rcu) to kfree_rcu()

The rcu callback __nf_ct_ext_free_rcu() just calls a kfree(),
so we use kfree_rcu() instead of the call_rcu(__nf_ct_ext_free_rcu).

Signed-off-by: Lai Jiangshan <[e-mail]>
Acked-by: David S. Miller <[e-mail]>
Signed-off-by: Paul E. McKenney <[e-mail]>
Reviewed-by: Josh Triplett <[e-mail]>

net/netfilter/nf_conntrack_extend.c

···
 	return (void *)(*ext) + off;
 }
 
-static void __nf_ct_ext_free_rcu(struct rcu_head *head)
-{
-	struct nf_ct_ext *ext = container_of(head, struct nf_ct_ext, rcu);
-	kfree(ext);
-}
-
 void *__nf_ct_ext_add(struct nf_conn *ct, enum nf_ct_ext_id id, gfp_t gfp)
 {
 	struct nf_ct_ext *old, *new;
···
 					(void *)old + old->offset[i]);
 			rcu_read_unlock();
 		}
-		call_rcu(&old->rcu, __nf_ct_ext_free_rcu);
+		kfree_rcu(old, rcu);
 		ct->ext = new;
 	}