virtio_net: Remove u64_stats_update_begin()/end() for stats fetch

This place is fetching the stats, u64_stats_update_begin()/end()
should not be used, and the fetcher of stats is in the same context
as the updater of the stats, so don't need any protection

Suggested-by: Jakub Kicinski <kuba@kernel.org>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Li RongQing <lirongqing@baidu.com>
Link: https://lore.kernel.org/20240621094552.53469-1-lirongqing@baidu.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>