tc-netem: fix limit description in man page

tc-netem: fix limit description in man page

As the kernel code says, limit is actually the amount of packets it can
hold queued at a time, as per:

static int netem_enqueue(struct sk_buff *skb, struct Qdisc *sch,
                         struct sk_buff **to_free)
{
	...
        if (unlikely(sch->q.qlen >= sch->limit))
                return qdisc_drop_all(skb, sch, to_free);

So lets fix the description of the field in the man page.

Signed-off-by: Marcelo Ricardo Leitner <mleitner@redhat.com>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>