tun: fix missing dropped counter in tun_xdp_act

The commit 8ae1aff0 ("tuntap: split out XDP logic") includes
dropped counter for XDP_DROP, XDP_ABORTED, and invalid XDP actions.
Unfortunately, that commit missed the dropped counter when error
occurs during XDP_TX and XDP_REDIRECT actions. This patch fixes
this issue.

Fixes: 8ae1aff0

 ("tuntap: split out XDP logic")
Signed-off-by: Yunjian Wang <wangyunjian@huawei.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>