espintcp: use datagram_poll_queue for socket readiness

espintcp uses a custom queue (ike_queue) to deliver packets to
userspace. The polling logic relies on datagram_poll, which checks
sk_receive_queue, which can lead to false readiness signals when that
queue contains non-userspace packets.

Switch espintcp_poll to use datagram_poll_queue with ike_queue, ensuring
poll only signals readiness when userspace data is actually available.

Fixes: e27cca9 ("xfrm: add espintcp (RFC 8229)")
Signed-off-by: Ralf Lici <ralf@mandelbit.com>
Reviewed-by: Sabrina Dubroca <sd@queasysnail.net>
Link: https://patch.msgid.link/20251021100942.195010-3-ralf@mandelbit.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Author: ralflici

net/xfrm/espintcp.c

@@ -555,14 +555,10 @@ static void espintcp_close(struct sock *sk, long timeout)
 static __poll_t espintcp_poll(struct file *file, struct socket *sock,
 			      poll_table *wait)
 {
-	__poll_t mask = datagram_poll(file, sock, wait);
 	struct sock *sk = sock->sk;
 	struct espintcp_ctx *ctx = espintcp_getctx(sk);
 
-	if (!skb_queue_empty(&ctx->ike_queue))
-		mask |= EPOLLIN | EPOLLRDNORM;
-
-	return mask;
+	return datagram_poll_queue(file, sock, wait, &ctx->ike_queue);
 }
 
 static void build_protos(struct proto *espintcp_prot,