tuntap: restore default qdisc

tuntap: restore default qdisc

After commit f84bb1eac027 ("net: fix IFF_NO_QUEUE for drivers using
alloc_netdev"), default qdisc was changed to noqueue because
tuntap does not set tx_queue_len during .setup(). This patch restores
default qdisc by setting tx_queue_len in tun_setup().

Fixes: f84bb1eac027 ("net: fix IFF_NO_QUEUE for drivers using alloc_netdev")
Cc: Phil Sutter <[email protected]>
Signed-off-by: Jason Wang <[email protected]>
Acked-by: Michael S. Tsirkin <[email protected]>
Acked-by: Phil Sutter <[email protected]>
Signed-off-by: David S. Miller <[email protected]>