xen-netfront: Add missing skb_mark_for_recycle

Notice that skb_mark_for_recycle() is introduced later than fixes tag in
commit 6a5bcd84 ("page_pool: Allow drivers to hint on SKB recycling").

It is believed that fixes tag were missing a call to page_pool_release_page()
between v5.9 to v5.14, after which is should have used skb_mark_for_recycle().
Since v6.6 the call page_pool_release_page() were removed (in
commit 535b9c61 ("net: page_pool: hide page_pool_release_page()")
and remaining callers converted (in commit 6bfef2ec ("Merge branch
'net-page_pool-remove-page_pool_release_page'")).

This leak became visible in v6.8 via commit dba1b8a7 ("mm/page_pool: catch
page_pool memory leaks").

Cc: stable@vger.kernel.org
Fixes: 6c5aa6fc ("xen networking: add basic XDP support for xen-netfront")
Reported-by: Leonidas Spyropoulos <artafinde@archlinux.com>
Link: https://bugzilla.kernel.org/show_bug.cgi?id=218654Reported-by: Arthur Borsboom <arthurborsboom@gmail.com>
Signed-off-by: Jesper Dangaard Brouer <hawk@kernel.org>
Link: https://lore.kernel.org/r/171154167446.2671062.9127105384591237363.stgit@firesoulSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/xen-netfront.c

@@ -285,6 +285,7 @@ static struct sk_buff *xennet_alloc_one_rx_buffer(struct netfront_queue *queue)
 		return NULL;
 	}
 	skb_add_rx_frag(skb, 0, page, 0, 0, PAGE_SIZE);
+	skb_mark_for_recycle(skb);
 
 	/* Align ip header to a 16 bytes boundary */
 	skb_reserve(skb, NET_IP_ALIGN);