xfrm: mark kmem_caches as __ro_after_init

Kmem caches aren't relocated once set up.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
index 7a23078..12bd415 100644
--- a/net/xfrm/xfrm_policy.c
+++ b/net/xfrm/xfrm_policy.c
@@ -51,7 +51,7 @@ static DEFINE_SPINLOCK(xfrm_policy_afinfo_lock);
 static struct xfrm_policy_afinfo const __rcu *xfrm_policy_afinfo[AF_INET6 + 1]
 						__read_mostly;
 
-static struct kmem_cache *xfrm_dst_cache __read_mostly;
+static struct kmem_cache *xfrm_dst_cache __ro_after_init;
 static __read_mostly seqcount_t xfrm_policy_hash_generation;
 
 static void xfrm_init_pmtu(struct xfrm_dst **bundle, int nr);