Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/drivers/net/xen-netback/hash.c b/drivers/net/xen-netback/hash.c
index 0ccb021..10d580c 100644
--- a/drivers/net/xen-netback/hash.c
+++ b/drivers/net/xen-netback/hash.c
@@ -454,6 +454,8 @@
 	if (xenvif_hash_cache_size == 0)
 		return;
 
+	BUG_ON(vif->hash.cache.count);
+
 	spin_lock_init(&vif->hash.cache.lock);
 	INIT_LIST_HEAD(&vif->hash.cache.list);
 }