Filter class output by classid

Filter class output by classid

Sometimes while dividing bandwidth by classes it is useful to see how some
specific class doing things live.

Which my simple patch it is possible to do
watch -n1 "tc -s -d class show dev eth0.2022 classid 1:1520"
and to get live statistics, how packets queued or dropped, and how much
bandwidth used (if estimator defined) for specific class.

Signed-off-by: Denys Fedoryshchenko <denys@visp.net.lb>