net: refactor bpf_sk_reuseport_detach()

Refactor sk_user_data dereference using more generic function
__rcu_dereference_sk_user_data_with_flags(), which improve its
maintainability

Suggested-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Hawkins Jiawei <yin31149@gmail.com>
Reviewed-by: Jakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

kernel/bpf/reuseport_array.c

@@ -21,14 +21,11 @@ static struct reuseport_array *reuseport_array(struct bpf_map *map)
 /* The caller must hold the reuseport_lock */
 void bpf_sk_reuseport_detach(struct sock *sk)
 {
-	uintptr_t sk_user_data;
+	struct sock __rcu **socks;
 
 	write_lock_bh(&sk->sk_callback_lock);
-	sk_user_data = (uintptr_t)sk->sk_user_data;
-	if (sk_user_data & SK_USER_DATA_BPF) {
-		struct sock __rcu **socks;
-
-		socks = (void *)(sk_user_data & SK_USER_DATA_PTRMASK);
+	socks = __rcu_dereference_sk_user_data_with_flags(sk, SK_USER_DATA_BPF);
+	if (socks) {
 		WRITE_ONCE(sk->sk_user_data, NULL);
 		/*
 		 * Do not move this NULL assignment outside of