af_packet: use swap() instead of the open coded macro XC()

	mutex_lock(&po->pg_vec_lock);

	mutex_lock(&po->pg_vec_lock);

	if (closing || atomic_read(&po->mapped) == 0) {

	if (closing || atomic_read(&po->mapped) == 0) {

		err = 0;

		err = 0;

#define XC(a, b) ({ __typeof__ ((a)) __t; __t = (a); (a) = (b); __t; })

		spin_lock_bh(&rb_queue->lock);

		spin_lock_bh(&rb_queue->lock);

		pg_vec = XC(rb->pg_vec, pg_vec);

		swap(rb->pg_vec, pg_vec);

		rb->frame_max = (req->tp_frame_nr - 1);

		rb->frame_max = (req->tp_frame_nr - 1);

		rb->head = 0;

		rb->head = 0;

		rb->frame_size = req->tp_frame_size;

		rb->frame_size = req->tp_frame_size;

		spin_unlock_bh(&rb_queue->lock);

		spin_unlock_bh(&rb_queue->lock);

		order = XC(rb->pg_vec_order, order);

		swap(rb->pg_vec_order, order);

		req->tp_block_nr = XC(rb->pg_vec_len, req->tp_block_nr);

		swap(rb->pg_vec_len, req->tp_block_nr);

		rb->pg_vec_pages = req->tp_block_size/PAGE_SIZE;

		rb->pg_vec_pages = req->tp_block_size/PAGE_SIZE;

		po->prot_hook.func = (po->rx_ring.pg_vec) ?

		po->prot_hook.func = (po->rx_ring.pg_vec) ?

						tpacket_rcv : packet_rcv;

						tpacket_rcv : packet_rcv;

		skb_queue_purge(rb_queue);

		skb_queue_purge(rb_queue);

#undef XC

		if (atomic_read(&po->mapped))

		if (atomic_read(&po->mapped))

			pr_err("packet_mmap: vma is busy: %d\n",

			pr_err("packet_mmap: vma is busy: %d\n",

			       atomic_read(&po->mapped));

			       atomic_read(&po->mapped));