Due to bugs in netem (fixed by later patches), it is possible to get qdisc
qlen to go negative. If this happens the CPU ends up spinning forever
in qdisc_run(). So add a BUG_ON() to trap it.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: David S. Miller <davem@davemloft.net>