ipv6: replace call_rcu by kfree_rcu for simple kmem_cache_free callback

ipv6: replace call_rcu by kfree_rcu for simple kmem_cache_free callback

Since SLOB was removed and since
commit 6c6c47b063b5 ("mm, slab: call kvfree_rcu_barrier() from kmem_cache_destroy()"),
it is not necessary to use call_rcu when the callback only performs
kmem_cache_free. Use kfree_rcu() directly.

The changes were made using Coccinelle.

Signed-off-by: Julia Lawall <Julia.Lawall@inria.fr>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Acked-by: Paul E. McKenney <paulmck@kernel.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Link: https://patch.msgid.link/20241013201704.49576-5-Julia.Lawall@inria.fr
Signed-off-by: Jakub Kicinski <kuba@kernel.org>