net: openvswitch: fix data race in ovs_vport_get_upcall_stats

net: openvswitch: fix data race in ovs_vport_get_upcall_stats

In ovs_vport_get_upcall_stats(), some statistics protected by
u64_stats_sync, are read and accumulated in ignorance of possible
u64_stats_fetch_retry() events. These statistics are already accumulated
by u64_stats_inc(). Fix this by reading them into temporary variables
first.

Fixes: 1933ea365aa7 ("net: openvswitch: Add support to count upcall packets")
Signed-off-by: David Yang <mmyangfl@gmail.com>
Acked-by: Ilya Maximets <i.maximets@ovn.org>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Aaron Conole <aconole@redhat.com>
Link: https://patch.msgid.link/20260121072932.2360971-1-mmyangfl@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>