tun: return NET_XMIT_DROP for dropped packets
tun: return NET_XMIT_DROP for dropped packets

After commit 5d097109257c03a71845729f8db6b5770c4bbedc
("tun: only queue packets on device"), NETDEV_TX_OK was returned for
dropped packets. This will confuse pktgen since dropped packets were
counted as sent ones.

Fixing this by returning NET_XMIT_DROP to let pktgen count it as error
packet.

Cc: Michael S. Tsirkin <255103e50249e3d658441816e0597170ebfc16ef@redhat.com>
Signed-off-by: Jason Wang <808efd45667dbd241e4e026b5673172419ecb43e@redhat.com>
Signed-off-by: David S. Miller <fe08d3c717adf2ae63592e4c9aec6e3e404d8e3e@davemloft.net>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs