net: ifdef struct sock::sk_async_wait_queue

Every user is under CONFIG_NET_DMA already, so ifdef field as well.
Signed-off-by: NAlexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/net/sock.h

@@ -239,7 +239,9 @@ struct sock {
 	int			sk_sndbuf;
 	struct sk_buff_head	sk_receive_queue;
 	struct sk_buff_head	sk_write_queue;
+#ifdef CONFIG_NET_DMA
 	struct sk_buff_head	sk_async_wait_queue;
+#endif
 	int			sk_wmem_queued;
 	int			sk_forward_alloc;
 	gfp_t			sk_allocation;