wireguard: device: leverage core stats allocator

With commit 34d21de9 ("net: Move {l,t,d}stats allocation to core
and convert veth & vrf"), stats allocation could be done on net core
instead of in this driver.

With this new approach, the driver doesn't have to bother with error
handling (allocation failure checking, making sure free happens in the
right spot, etc). This is core responsibility now.

Remove the allocation in this driver and leverage the network core
allocation instead.
Signed-off-by: Breno Leitao <leitao@debian.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

drivers/net/wireguard/device.c

@@ -262,7 +262,6 @@ static void wg_destruct(struct net_device *dev)
 	rcu_barrier(); /* Wait for all the peers to be actually freed. */
 	wg_ratelimiter_uninit();
 	memzero_explicit(&wg->static_identity, sizeof(wg->static_identity));
-	free_percpu(dev->tstats);
 	kvfree(wg->index_hashtable);
 	kvfree(wg->peer_hashtable);
 	mutex_unlock(&wg->device_update_lock);
@@ -297,6 +296,7 @@ static void wg_setup(struct net_device *dev)
 	dev->hw_enc_features |= WG_NETDEV_FEATURES;
 	dev->mtu = ETH_DATA_LEN - overhead;
 	dev->max_mtu = round_down(INT_MAX, MESSAGE_PADDING_MULTIPLE) - overhead;
+	dev->pcpu_stat_type = NETDEV_PCPU_STAT_TSTATS;
 
 	SET_NETDEV_DEVTYPE(dev, &device_type);
 
@@ -331,14 +331,10 @@ static int wg_newlink(struct net *src_net, struct net_device *dev,
 	if (!wg->index_hashtable)
 		goto err_free_peer_hashtable;
 
-	dev->tstats = netdev_alloc_pcpu_stats(struct pcpu_sw_netstats);
-	if (!dev->tstats)
-		goto err_free_index_hashtable;
-
 	wg->handshake_receive_wq = alloc_workqueue("wg-kex-%s",
 			WQ_CPU_INTENSIVE | WQ_FREEZABLE, 0, dev->name);
 	if (!wg->handshake_receive_wq)
-		goto err_free_tstats;
+		goto err_free_index_hashtable;
 
 	wg->handshake_send_wq = alloc_workqueue("wg-kex-%s",
 			WQ_UNBOUND | WQ_FREEZABLE, 0, dev->name);
@@ -397,8 +393,6 @@ static int wg_newlink(struct net *src_net, struct net_device *dev,
 	destroy_workqueue(wg->handshake_send_wq);
 err_destroy_handshake_receive:
 	destroy_workqueue(wg->handshake_receive_wq);
-err_free_tstats:
-	free_percpu(dev->tstats);
 err_free_index_hashtable:
 	kvfree(wg->index_hashtable);
 err_free_peer_hashtable: