MEDIUM: bwlim: Add support of bandwith limitation at the stream level

MEDIUM: bwlim: Add support of bandwith limitation at the stream level

This patch adds a filter to limit bandwith at the stream level. Several
filters can be defined. A filter may limit incoming data (upload) or
outgoing data (download). The limit can be defined per-stream or shared via
a stick-table. For a given stream, the bandwith limitation filters can be
enabled using the "set-bandwidth-limit" action.

A bandwith limitation filter can be used indifferently for HTTP or TCP
stream. For HTTP stream, only the payload transfer is limited. The filter is
pretty simple for now. But it was designed to be extensible. The current
design tries, as far as possible, to never exceed the limit. There is no
burst.