tun: replace get_cpu_ptr with this_cpu_ptr when bh disabled

tun_xdp_one() runs with local bh disabled. So there is no need to
disable preemption by calling get_cpu_ptr while updating stats. This
patch replaces the use of get_cpu_ptr() with this_cpu_ptr() as a
micro-optimization. Also removes related put_cpu_ptr call.
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Prashant Bhole <bhole_prashant_q7@lab.ntt.co.jp>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/tun.c

@@ -2495,12 +2495,14 @@ static int tun_xdp_one(struct tun_struct *tun,
 	skb_record_rx_queue(skb, tfile->queue_index);
 	netif_receive_skb(skb);
 
-	stats = get_cpu_ptr(tun->pcpu_stats);
+	/* No need for get_cpu_ptr() here since this function is
+	 * always called with bh disabled
+	 */
+	stats = this_cpu_ptr(tun->pcpu_stats);
 	u64_stats_update_begin(&stats->syncp);
 	stats->rx_packets++;
 	stats->rx_bytes += datasize;
 	u64_stats_update_end(&stats->syncp);
-	put_cpu_ptr(stats);
 
 	if (rxhash)
 		tun_flow_update(tun, rxhash, tfile);