net: respect GFP_DMA in __netdev_alloc_skb()

Few drivers use GFP_DMA allocations, and netdev_alloc_frag()
doesn't allocate pages in DMA zone.
Signed-off-by: NEric Dumazet <edumazet@google.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/core/skbuff.c

@@ -353,7 +353,7 @@ struct sk_buff *__netdev_alloc_skb(struct net_device *dev,
 	unsigned int fragsz = SKB_DATA_ALIGN(length + NET_SKB_PAD) +
 			      SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
 
-	if (fragsz <= PAGE_SIZE && !(gfp_mask & __GFP_WAIT)) {
+	if (fragsz <= PAGE_SIZE && !(gfp_mask & (__GFP_WAIT | GFP_DMA))) {
 		void *data = netdev_alloc_frag(fragsz);
 
 		if (likely(data)) {