After commit 8ffab51b
(macvlan: lockless tx path), tx stat counter were converted to percpu stat
structure. So we need use to this also for tx_dropped in macvtap. Otherwise, the
management won't notice the dropping packet in macvtap tx path.

Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Vlad Yasevich <vyasevic@redhat.com>
Cc: Eric Dumazet <edumazet@google.com>
Signed-off-by: NJason Wang <jasowang@redhat.com>
Acked-by: NMichael S. Tsirkin <mst@redhat.com>
Acked-by: NVlad Yasevich <vyasevic@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>