distributor: add new burst-capable library

distributor: add new burst-capable library

This patch includes the code for new burst-capable distributor library.

It also includes the rte_distributor_next.h file which will
be used as the public header once we add in the symbol versioning
for v20 and v1705 APIs, at which stage we will rename it to
rte_distributor.h.

The new distributor code contains a very similar API to the legacy code,
but now sends bursts of up to 8 mbufs to each worker. Flow ID's are
reduced to 15 bits for an optimal flow matching algorithm.

Signed-off-by: David Hunt <david.hunt@intel.com>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>