skbuff: Replace open-coded skb_propagate_pfmemalloc()s

Use skb_propagate_pfmemalloc() in build_skb()/build_skb_around() instead
of open-coding it.
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Gal Pressman <gal@nvidia.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/core/skbuff.c

@@ -422,8 +422,7 @@ struct sk_buff *build_skb(void *data, unsigned int frag_size)
 
 	if (skb && frag_size) {
 		skb->head_frag = 1;
-		if (page_is_pfmemalloc(virt_to_head_page(data)))
-			skb->pfmemalloc = 1;
+		skb_propagate_pfmemalloc(virt_to_head_page(data), skb);
 	}
 	return skb;
 }
@@ -445,8 +444,7 @@ struct sk_buff *build_skb_around(struct sk_buff *skb,
 
 	if (frag_size) {
 		skb->head_frag = 1;
-		if (page_is_pfmemalloc(virt_to_head_page(data)))
-			skb->pfmemalloc = 1;
+		skb_propagate_pfmemalloc(virt_to_head_page(data), skb);
 	}
 	return skb;
 }