ofproto-dpif: Added Per backer recirculation ID management

Recirculation ID needs to be unique per datapath. Its usage will be
tracked by the backer that corresponds to the datapath.

In theory, Recirculation ID can be any uint32_t value, except 0. This
implementation limits to a smaller range just for ease of debugging.
Make the range size 0 effectively disables recirculation.

Signed-off-by: Andy Zhou <azhou@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>