tun: avoid unnecessary READ_ONCE in tun_net_xmit

The statement no longer serves a purpose.

Commit fa35864e ("tuntap: Fix for a race in accessing numqueues")
added the ACCESS_ONCE to avoid a race condition with skb_queue_len.

Commit 436acceb ("tuntap: remove unnecessary sk_receive_queue
length check during xmit") removed the affected skb_queue_len check.

Commit 96f84061 ("tun: add eBPF based queue selection method")
split the function, reading the field a second time in the callee.
The temp variable is now only read once, so just remove it.
Signed-off-by: NWillem de Bruijn <willemb@google.com>
Acked-by: NJason Wang <jasowang@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/tun.c

@@ -990,14 +990,12 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev)
 	struct tun_struct *tun = netdev_priv(dev);
 	int txq = skb->queue_mapping;
 	struct tun_file *tfile;
-	u32 numqueues = 0;
 
 	rcu_read_lock();
 	tfile = rcu_dereference(tun->tfiles[txq]);
-	numqueues = READ_ONCE(tun->numqueues);
 
 	/* Drop packet if interface is not attached */
-	if (txq >= numqueues)
+	if (txq >= tun->numqueues)
 		goto drop;
 
 	if (!rcu_dereference(tun->steering_prog))