netmem, devmem, tcp: access pp fields through @desc in net_iov

Convert all the legacy code directly accessing the pp fields in net_iov
to access them through @desc in net_iov.

Signed-off-by: Byungchul Park <[e-mail]>
Signed-off-by: Jakub Kicinski <[e-mail]>

include/linux/skbuff.h

···
 					    enum dma_data_direction dir)
 {
 	if (skb_frag_is_net_iov(frag)) {
-		return netmem_to_net_iov(frag->netmem)->dma_addr + offset +
-		       frag->offset;
+		return netmem_to_net_iov(frag->netmem)->desc.dma_addr +
+		       offset + frag->offset;
 	}
 	return dma_map_page(dev, skb_frag_page(frag),
 			    skb_frag_off(frag) + offset, size, dir);

net/core/devmem.c

···
 	index = offset / PAGE_SIZE;
 	niov = &owner->area.niovs[index];
 
-	niov->pp_magic = 0;
-	niov->pp = NULL;
-	atomic_long_set(&niov->pp_ref_count, 0);
+	niov->desc.pp_magic = 0;
+	niov->desc.pp = NULL;
+	atomic_long_set(&niov->desc.pp_ref_count, 0);
 
 	return niov;
 }

net/ipv4/tcp.c

···
 				if (err)
 					goto out;
 
-				atomic_long_inc(&niov->pp_ref_count);
+				atomic_long_inc(&niov->desc.pp_ref_count);
 				tcp_xa_pool.netmems[tcp_xa_pool.idx++] = skb_frag_netmem(frag);
 
 				sent += copy;