linux: generic: qdisc: use priv->limit instead of qdisc->limit
linux: generic: qdisc: use priv->limit instead of qdisc->limit

This is to avoid conditional code, since kernel versions < 2.6.39
do not have qdisc->limit.

luigirizzo/netmap,luigirizzo/netmap,luigirizzo/netmap,luigirizzo/netmap,luigirizzo/netmap