tc: netem rate shaping and cell extension

This patch add rate shaping as well as cell support. The link-rate can be
specified via rate options. Three optional arguments control the cell
knobs: packet-overhead, cell-size, cell-overhead. To ratelimit eth0 root
queue to 5kbit/s, with a 20 byte packet overhead, 100 byte cell size and
a 5 byte per cell overhead:

	tc qdisc add dev eth0 root netem rate 5kbit 20 100 5

Signed-off-by: Hagen Paul Pfeifer <hagen@jauu.net>